4¢PhytoKeys PhytoKeys 259: 1-25 (2025) DOI: 10.3897/phytokeys.259.157847 Research Article Rhizophora stylosa (Rhizophoraceae) newly recorded from Thailand: lectotypification, leaf anatomy, and pollen morphology Chatchai Ngernsaengsaruay’”©, Nittaya Mianmit®®, Supol Kamsanor’*, Rachanee_ Pothitan®, Vipak Jintana®®, Nirat Jintana5, Pichet Chanton®®, Apinya Sukantatul', Jutiporn Khade* an oOo FP WO NYS Department of Botany, Faculty of Science, Kasetsart University, Chatuchak, Bangkok 10900, Thailand Biodiversity Center, Kasetsart University (BDCKU), Chatuchak, Bangkok 10900, Thailand Department of Forest Management, Faculty of Forestry, Kasetsart University, Chatuchak, Bangkok, 10900, Thailand Mu Ko Phetra National Park, Department of National Parks, Wildlife and Plant Conservation, Pak Nam Subdistrict, La-Ngu District, Satun Province, 91110, Thailand Department of National Parks, Wildlife and Plant Conservation, Chatuchak, Bangkok, 10900, Thailand Suan Luang Rama IX Foundation, Nong Bon Subdistrict, Prawet District, Bangkok, 10250, Thailand Corresponding authors: Nittaya Mianmit (ffornym@ku.ac.th); Supol Kamsanor (pol_k63@hotmail.com) OPEN Qaceess Academic editor: Alexander Sennikov Received: 4 May 2025 Accepted: 28 May 2025 Published: 17 June 2025 Citation: Ngernsaengsaruay C, Mianmit N, Kamsanor S, Pothitan R, Jintana V, Jintana N, Chanton P Sukantatul A, Khade J (2025) Rhizophora stylosa (Rhizophoraceae) newly recorded from Thailand: lectotypification, leaf anatomy, and pollen morphology. PhytoKeys 259: 1-25. https://doi.org/10.3897/ phytokeys.259.157847 Copyright: © Chatchai Ngernsaengsaruay et al. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International - CC BY 4.0). Abstract Rhizophora stylosa (Rhizophoraceae), previously known from India (Andaman and Nico- bar Islands), China to Indo-China, and the Pacific Island, is reported here as a new record from coastal areas with muddy-sandy, sandy or sandy-rocky substrates at Ko Lidi and Ko Bulon Le, within Mu Ko Phetra National Park, La-ngu District, and at Ao Talo Wao, Ko Taru- tao, Tarutao National Park, Mueang Satun District, Satun Province, Peninsular Thailand. A detailed morphological description, illustrations and a distribution map of the species are provided, along with notes on distribution, habitat and ecology, phenology, a preliminary conservation assessment, etymology and specimens examined. In addition, Rhizophora stylosa is lectotypified, the Thai vernacular name “Kongkang phetra” is herein proposed for this species, and an updated identification key to the species of Rhizophora in Thailand is presented. The species is currently assessed as Least Concern [LC] under the IUCN con- servation status. Furthermore, detailed descriptions of leaf anatomical features and pol- len morphology are provided. The thick cuticles, sunken stomata, large hypodermal cells, and cork warts are adaptive anatomical features of leaves in Rhizophora that live in the mangrove environments. The pollen grains of Rhizophora stylosa are tricolporate, prolate spheroidal or oblate spheroidal shapes, small-sized, and reticulate exine sculpturing. Key words: Lectotypification, Malpighiales, morphology, palynology, plant anatomy, red mangrove, Rhizophoreae, taxonomy, true mangrove tree, vivipary Introduction Rhizophoraceae Pers. is well known as the most species-rich mangrove family, comprising four exclusively mangrove genera and 19 species: Bruguiera Lam. ex Savigny (six species and two natural hybrids), Ceriops Arn. (five species), Kandelia (DC.) Wight & Arn. (two species), and Rhizophora L. (six species and five natural hybrids) (Tomlinson 1986, 2016; Sheue et al. 2012; POWO 2025; WFO 2025). All members of the Rhizophoraceae have large, conspicuous, gla- brous and caducous interpetiolar stipules on both vegetative and reproductive Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand shoots, which strongly ensheath the developing leaves and inflorescences (Hou 1958). In species of mangrove Rhizophoraceae, several to hundreds of aggregated finger-like colleters mixed with milky mucilage can be observed with the naked eye at the adaxial base of the stipules (Tomlinson 1986, 2016; Sheue 2003). The structural and mechanical protection provided by stipules and colleter exudates may help shield the young shoots of these mangrove plants from their harsh environmental conditions (Sheue et al. 2012). The tribe Rhizophoreae Bartl. is characterized by the following features: true mangrove shrubs or trees, with aerial roots; glabrous and caducous interpeti- olar stipules that sheath the terminal bud and young leaves; decussate, entire leaves; cymose inflorescences; 4-—16-merous flowers; mostly diplostemonous androecia (with twice as many stamens as petals); half-inferior to fully inferior ovaries, 2-3-carpellate with two ovules per carpel; baccate, fibrous fruits usu- ally containing a single seed; and viviparous germination. This pantropical tribe comprises four genera: Bruguiera, Ceriops, Kandelia, and Rhizophora (Henslow 1878; King 1897; Hou 1958; Schwarzbach 2014). Rhizophora is a group of tropical and subtropical mangrove trees, com- monly referred to as true mangroves. It is a small genus belonging to the or- der Malpighiales Juss. ex Bercht. & J. Presl, the family Rhizophoraceae (The Angiosperm Phylogeny Group 2016), and the tribe Rhizophoreae (Schwarzbach 2014). Eleven taxa have been recognized within the genus, comprising six ac- cepted species and five natural hybrids. Among these, two species and one hy- brid occur in the Americas; three species and one hybrid in Africa; three species and two hybrids in the Indian subcontinent, China, and Southeast Asia (POWO 2025); three species and one hybrid in Australia (Duke and Bunt 1979; McCusk- er 1984; POWO 2025); and four species and three hybrids in the Pacific region (Melanesia, Micronesia, and Polynesia) (Tomlinson 1978; POWO 2025). These three species of Rhizophora found in the Indian subcontinent, China, and South- east Asian species are R. apiculata Blume, R. mucronata Poir., and R. stylosa Griff. (Hou 1958, 1960; Qin and Boufford 2007; Marchand 2008; POWO 2025). In addition, two natural hybrids occur in the region: R. x annamalayana Kathire- san (R. apiculata x R. mucronata) and R. x lamarckii Montrouz. (R. apiculata x R. stylosa) (Parani et al. 1997; Ng and Chan 2012; Ng et al. 2013; Setyawan et al. 2014; Ragavan et al. 2015; POWO 2025). Previously, Hou (1970) treated the genus Rhizophora in the “Flora of Thailand”, recognizing two species: R. apiculata and R. mucronata. However, this account was brief, providing limited morphological descriptions and lacking other supporting information. Recently, Ngernsaengsaruay et al. (2024) revised the genus Rhizophora for Thailand, offering updated and detailed morphological descriptions, an identification key, and comprehensive notes on distribution, habitat and ecology, phenology, conservation assessments, and lectotypifica- tions. In addition, leaf anatomical characters and pollen morphology were ex- amined to provide a complete overview of Rhizophora in Thailand. In 2007, Mr.Nirat Jintana and Associate Professor Dr.Vipak Jintana discov- ered a plant belonging to the genus Rhizophora on Ko Lidi and Ko Bulon Le, within Mu Ko Phetra National Park, La-ngu District, Satun Province. However, no specimens were collected at the time, and the species remain unidentified. During fieldwork conducted at the same locations in April 2025, and at Ao Talo Wao, Ko Tarutao, Tarutao National Park, Mueang Satun District, Satun Province PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 9 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand in May 2025, we collected specimens bearing both vegetative and reproductive parts. These specimens match the type and descriptions found in various tax- onomic references of Rhizophora stylosa Griff. (e.g., Griffith 1854; Hou 1958; Backer and Bakhuizen van den Brink 1963; Duke and Bunt 1979), a species previously recorded from India, China to Indo-China, and the Pacific, but not Thailand. Consequently, this represents a new record for Thailand. A detailed morphological description, illustrations, lectotypification, and an updated iden- tification key to the species of Rhizophora in Thailand are provided, along with notes on distribution, habitat and ecology, phenology, preliminary conservation assessment, etymology, vernacular name and specimens examined. Addition- ally, leaf anatomical characteristics and pollen morphology are presented. Materials and methods Plant specimens of Rhizophora stylosa were observed and collected in the pen- insular region of Thailand. The collected specimens were identified by consult- ing taxonomic literature (e.g., Griffith 1854; Henslow 1878; Ridley 1922; Hou 1958, 1960; Backer and Bakhuizen van den Brink 1963; Tomlinson 1978; Duke and Bunt 1979; McCusker 1984; Qin and Boufford 2007; Duke 2010; Ng and Chan 2012; Setyawan et al. 2014; Ragavan 2015; Ragavan et al. 2015, 2021; Kannan et al. 2021) and by comparison with herbarium specimens housed in the following herbaria: BK, BKF, as well as those available through the virtu- al herbarium databases of A, BR, CAL, E, K, L, PR SING, US, and GBIF (https:// www.gbif.org/). All herbarium codes follow Thiers (2025, continuously updat- ed). The taxonomic history of the species was compiled from both published literature and online databases (IPNI 2025; POWO 2025; WFO 2025). Morpho- logical characters, distribution, habitat and ecology, phenology, and uses were described based on newly collected herbarium specimens and the author’s field observations. The distribution map was generated using the R program, based on data from the specimen examined and credible literature sources (e.g., Ragavan 2015; Kannan et al. 2021; Ragavan et al. 2021). Conservation status was assessed according to the IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee 2024), supplemented with GeoCAT analysis (Bachman et al. 2011) and field data. The leaf anatomical features of Rhizophora stylosa were investigated through transverse sectioning using a sliding microtome at thickness of 15-20 um. To study the epidermal cells, the leaves were peeled and mounted. Permanent slides were prepared according to the standard methods described by Johan- sen (1940) and Kermanee (2008). Anatomical characteristics were observed and recorded photographically using an Olympus BX53 microscope equipped with an Olympus DP74 digital camera at the Department of Botany, Faculty of Science, Kasetsart University (KU). Anatomical terminology follows the con- ventions outlined by Metcalfe and Chalk (1957). Samples of pollen grains were examined and recorded photographically us- ing an Olympus BX53 microscope equipped with an Olympus DP74 digital cam- era. For scanning electron microscopy (SEM), materials were prepared at the Scientific Equipment Centre, Faculty of Science, Kasetsart University, by mount- ing the pollen grains on stubs with double-sided sellotape, sputter-coating them with gold, and examining them using an FEI Quanta 450 SEM (Hillsboro, PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 3 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand OR, USA) at 15.00 kV. The characteristics of the pollen grains were examined and measured following the methods of Erdtman (1945, 1952) and Simpson (2010). Pollen morphology terminology follows that of Punt et al. (2007). Results and discussion Taxonomic treatment Rhizophora stylosa Griff., Not. Pl. Asiat. 4: 665. 1854; G. Hensl. in Hook. f., FI. Brit. India 2: 436. 1878; Ridl., Fl. Malay Penins. 1: 693. 1922; Ding Hou, FI. Males., Ser. 1, Spermat. 5(4): 456, figs. 5, 8a—-f, 13. 1958 et Blumea 10(2): 629. 1960; Backer & Bakh. f., Fl. Java 1: 380. 1963; Toml., J. Arnold Arbor. 59: 163, figs. 3, 4D-F. 1978; N. C. Duke & J. S. Bunt, Aust. J. Bot. 27: 672. fig. 6a- b. 1979; A. McCusker in A. S. George et al., Fl. Australia 22: 2. 1984; W. Giesen et al., Mangrove Guideb. S.E. Asia: 239, fig. 239. 2007; H. Qin & Boufford, FI. China 13: 296, fig. 316(1—9). 2007; N. C. Duke, Blumea 55: 179, fig. 8. 2010; A. D. Setyawan et al., Nusantara Bioscience 6(1): 77, figs. 6A.b—G.b, 8. 2014; Ragavan, Taxon. Mangroves Andaman and Nicobar Isl. PhD Thesis: 115, fig. 43. 2015; Ragavan et al., Indian Mangroves: 122-123. 2021; S. Kannan et al., Bot. Mar. 64(3): 7-8, figs. 3D, 5B, D, F, G, J, L, M (right), O, 2021. FIGSaI po = Rhizophora mucronata Poir. var. stylosa (Griff.) A. Schimp., Bot. Mitt. Tropen 3: 92. 1891; Guillaumin in Lecomte et al., Fl. Indo-Chine 2(6): 724. 1920. Type. Peninsular Malaysia * Malacca (Melaka, Malay), s.d., W. Griffth s.n. (lecto- type K digital image! [K005752944] (Fig. 5A), designated here; isolectotype: BR digital image! [BRO000031831338] (Fig. 5B). Description. Habit small evergreen trees, single- to multi-stemmed, 2.5—8 m tall, 10-60 cm GBH. Stilt roots much-branched, descending from the base of the stem, bearing numerous lenticels. Branches and branchlets decussate, growing upward at acute angles; branches often with pendulous aerial roots; branchlets terete, glabrous, with conspicuous annular stipular scars and leaf scars at the nodes. Bark grayish brown or dark brown, varies from smooth, rough or shallowly longitudinally and transversely fissured. Stipules interpetiolar, in pairs enclosing the young shoot (including the terminal bud and young leaves) and young inflo- rescences, pale green or green, turning whitish pale green or creamish white be- fore the leaves emerging or before falling off, reddish brown when dry, linear-lan- ceolate, gradually narrowing towards the apex, 3.5-7.5 cm long, 2.5-9 mm diam. at the base, apex acute, glabrous and caducous, outline in transverse section depressed orbicular basally and suborbicular to orbicular apically, with dense colleters aggregated in a basal band, producing a sticky white exudate; colleters sessile, pale yellow, narrowly conical, 0.5-1.2 mm long, 0.2—-0.5 mm diam. at the base, apex obtuse. Leaves decussate and crowded at the apical part of branch- lets, elliptic, 8-16 x 3-8.5 cm, apex mucronate, a short terminal stiff point pale green, turning black before they come off, 2-6 mm long, base cuneate, margin en- tire, coriaceous, shiny dark green above, pale green below, glabrous on both sur- faces, with numerous conspicuous, scattered tiny black cork warts below, midrib pale green (paler than lamina), flattened above, raised below, secondary veins PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 ri Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand 1cm 11cm 0.5cm 0.5cm 0.5cm 0.5cm icm 1com 0.5cm 0.5 cm G H K | Figure 1. Rhizophora stylosa. A, B. Flowering branchlets showing a terminal interpetiolar stipule, leaves, and inflorescenc- es with flower buds and fully open flowers; C. Flower buds; D. Flower bud in transverse section; E. Fully open flower in lateral view; F. Fully open flower in top view; G. Flower bud showing stamens with sepals and petals removed; H. Flower bud in longitudinal section; I. Sepals; J. Petals with densely long-villous along margins; K. Stamen; L-M. Pistils showing a long style; N-O. Fruits showing successive stages in development of hypocotyl. Drawn by Wanwisa Bhuchaisri. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Figure 2. Rhizophora stylosa. A-D. Habitats and habit; E. Stems supported by numerous branched stilt roots; F. Stem, outer bark and inner bark; G. Leaves showing adaxial and abaxial surfaces: Population A (left) and Population B (right); H. Branchlets, leaves and young inflorescences; I. Leaf scar with many tiny vascular bundle strands, arranged in a cres- cent moon; J. Stipule with dense colleters aggregated in a basal band, producing a sticky white exudate. Photos: Chatchai Ngernsaengsaruay (A-C, E-J) and Rachanee Pothitan (D). PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 6 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Figure 3. Rhizophora stylosa. A, B. Flowering branchlets showing inflorescences with flower buds and fully open flow- ers; C. Flowering branchlets showing flower buds and fully open flowers and fruiting branchlet showing young fruits; D. Inflorescence with flower buds and fully open flower; E, G. Flowering and fruiting branchlets showing leaves, inflores- cences with flower buds and fully open flowers, and hypocotyls. F. Seedling. Photos: Chatchai Ngernsaengsaruay. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 7 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand a8 a | | | oo a387 i) tl lea : BS + | | xz Te et a ee ‘GnEay ane a | i | di AX B a Ar wae he PTTitit te. Tr 2 P ah Se oe ee Os S88 ec 0888 eee et tt i yt Figure 4. Rhizophora stylosa. A. Fully open flower; B. Flower bud in longitudinal section; C. Flower bud in transverse sec- tion; D. Dissected flower showing sepals, petals, stamens, and pistil; E-G. Sepals; H-J. Petals with densely long-villous along margins; K-N. Stamens; O. Pistil showing a long style. Photos: Pichet Chanton (A-N), Apinya Sukantatul (0). PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 9 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand =| 3 iS) cae ie) is) is) copyright reserved iy Kot vised for Flora Malesiana Rhizophora stylosa Griff. de. DING HOU A hes & ujnquaqueld ad Figure 5. Lectotype and isolectotype of Rhizophora stylosa from Malacca, Peninsular Malaysia. A. Lectotype, W. Griffth s.n. (K [K005752944]); B. Isolectotype, W. Griffth s.n. (BR [BR0000031831338]). Photos: © The Board of Trustees of the RBG, Kew, https://records.data.kew.org/occurrences/f573f797-57cc-48c7-b444-c6a9b8f085c3 (A), Meise Botanic Gar- den, Meise, Belgium, https://www.botanicalcollections.be/specimen/BR0000031831338 (B). 8-14 on each side, curving towards the margin and connected in distinct loops and united into an intramarginal vein, visible above, obscure below, with inter- secondary veins, veinlets reticulate, visible above, obscure below; petioles green, 2-4.8 cm long, 2-4.5 mm diam., glabrous; fresh leaves brittle when crushed; young leaves shiny pale green; mature leaves turning greenish bright yellow and bright yellow before falling off; dry leaves yellowish brown. Inflorescences ax- illary, opposite, compound dichasia, dichotomously branched, 4—13-flowered cymes, 5-12.5 cm long; peduncles pale green, 2.3-—6 cm long, 2-3.5 mm diam., glabrous. Bracts 2, pale green, concave, 2.5-4 x 2.7-3.5 mm, apex rounded. Bracteoles at the base of the flower, pale green, connate at the base, bilobed, 3-5 x 4-6 mm. Flowers 4-merous; flower buds pale green, turning pale yellow when mature, ovoid or conical-ovoid, 0.9-1.5 cm long, 4-8 mm diam., apex obtuse; fully open flowers 1.2-1.8 cm diam.; sepals 4, erect or patent after anthesis, pale yellow on both sides, triangular, 0.7-1.3 cm x 4-6 mm, apex acute, coriaceous, glabrous; petals 4, creamish white, narrowly elliptic or elliptic, 0.6-1 cm x 1.5- 3.5 mm, thin, involute, densely long-villous along margins; stamens 8, 4 antese- palous and 4 antepetalous (each petal enclosing 1 stamen in flower buds); an- thers falcate-like, 3.5-8.5 x 1.2-2.8 mm, apex mucronate, triangular in outline in transverse section; filaments very short; free part of the ovary 0.7-1.2 mm long, PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 9 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand 1.2-1.8 mm diam.; style 3-5 mm long; stigma 2-lobed; pedicels pale green, 0.6-1 cm long, 2-3 mm diam. Fruits brownish green, greenish brown or brown, ovoid or conical-ovoid, 2-2.7 cm long, 1-1.7 cm diam. at the base, apex obtuse (before seed germination); obpyriform, 2.2-4 cm long, 1.7-3 cm diam. at the basal part, 0.9-1.7 cm diam. at the apical part (when the hypocotyls nearly come off), roughened surface; persistent sepals reflexed, triangular, 0.9-1.1 cm x 5-8.5 mm; infructescence stalks 2-6 cm long, 2-3 mm diam; fruit stalks 0.6- 1.7 cm long, 3-5 mm diam. Seeds 1, viviparous. Hypocotyls green, slightly glossy, cylindrical-clavate, 19.5-40 cm long, 6.5-9 mm diam. at the apical part, 1-1.6 cm diam. at the widest part, 0.8-1.3 cm diam. at the basal part, acute at the basal end, roughened surface, with numerous, scattered lenticels; cotyledon- ous cylindrical tubes pale green or greenish pale yellow, 0.6-1.2 cm diam. (can be seen when the hypocotyls nearly falling off). The measurements of the vegetative and reproductive parts of Rhizophora stylosa in Thailand are presented in Table 1. Distribution. India (Andaman and Nicobar Islands), China (South Guangxi, South Guangdong, Hainan), Taiwan (Taipei), Japan (Ryukyu Islands, also known as Nansei-shoto), Vietnam, Cambodia, Peninsular Thailand, Peninsular Malay- sia (also called Malaya), Singapore, Indonesia [Java, Lesser Sunda Islands, Sulawesi (also called Celebes), Moluccas (also called Maluku)], Philippines, Australia (Northern Territory, Queensland, New South Wales, Western Austra- lia), Melanesia (Bismarck Archipelago, New Guinea, Solomon Islands, Vanuatu, Fiji, New Caledonia), Micronesia (Mariana Islands, Caroline Islands, Gilbert Is- lands), Polynesia (Tuvalu, Tonga, Society Islands) (Fig. 6). Latitude (N) oa 125 Longitude (E) 150 100 Figure 6. Distribution of Rhizophora stylosa. It is widely distributed from India (Andaman and Nicobar Islands), China to Indo-China, and the Pacific Islands. In Thailand, this species is known only from Ko Lidi and Ko Bulon Le within Mu Ko Phetra National Park, located in La-ngu District, and from Ao Talo Wao, Ko Tarutao, in Tarutao National Park, Mueang Satun District, Satun Province. Map: Pichet Chonton & Chatchai Ngernsaengsaruay. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 10 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Table 1. Measurements of the vegetative and reproductive parts of Rhizophora stylosa in Thailand. Measurements of vegetative and reproductive parts (units) Sample sizes Ranges Mean + SD Stipule length (cm) 80 oles haa Os 5.40 + 0.92 Stipule diameter at the base (mm) 80 25-9:0 4.20 + 1.58 Colleter length (mm) 50 O5F12 0.72 + 0.16 Colleter diameter at the base (mm) 50 0.2-0,5 0.35 + 0.08 Leaf length (cm) 300 8.0-16.0 11.43 + 1.64 Leaf width (cm) 300 3.0-8.5 5.20 + 1.02 Leaf length/width ratio 300 Mee +29 2.22 + 0.19 Leaf lamina apex length (mm) 150 2.0-6.0 4.30 + 1.04 Number of secondary veins each side | 300 8-14 11.20 + 1.68 Petiole length (cm) 300 2.0-4.8 3.25+0.55 Petiole diameter at the middle (mm) 300 2.0-4.5 3.19 + 0.44 Inflorescence length (cm) 180 50-125 7:93 41.35 Peduncle length (cm) 180 2.3-6.0 3.80 + 0.82 Peduncle diameter at the middle (mm) 180 FARIS 2.54 + 0.34 Number of flowers per inflorescence 180 4-13 6.70 + 1.57 Mature flower bud length (cm) 200 Org 125 1.25 +0.10 Mature flower bud diameter at the basal part (cm) 200 4.0-8.0 6.41 + 0.82 Mature flower bud length/diameter ratio 200 Sane 1,97 £0.23 Fully open flower diameter (cm) 100 12-138 1.47+0.15 Sepal length (cm) 200 OF=183 1.01+0.14 Sepal width at the base (mm) 200 4.0-6.0 4.89 + 0.59 Sepal length/width ratio 200 W7H2,2 2.06 + 0.19 Petal length (cm) 200 0.6-1.0 0.79 +0.12 Petal width at the middle (cm) | 200 15-35 2.30 + 0.51 Petal length/width ratio 200 222574 3.51 4:00:62 Anther length (mm) 200 3.5=8.5 6.14+1.14 Anther width at the middle (mm) 200 a eae ae 1.70 + 0.40 Free part of the ovary length (mm) 100 07-182 0.97+0.12 Free part of the ovary diameter (mm) 100 teat Be 1.47+0.15 Style length (mm) 170 3.0-5.0 3.80 + 0.52 Pedicel length (cm) 100 0.6-1.0 0.82 +0.14 Pedicel diameter (mm) 100 2.0-3.0 2.58 + 0.26 Fruit length (cm) (hypocotyls nearly come off) 70 2.2-4.0 2.91 + 0.43 Fruit diameter at the basal part (cm) 70 iLZ=3:0 2.04 + 0.23 Fruit diameter at the apical part (cm) 70 0.9-1.7 1.04 + 0.17 Persistent sepal length (cm) 150 0.9-1.1 0.98 + 0.04 Persistent sepal width at the base (mm) 150 5.0-8.5 6.49 + 0.67 Infructescence stalk length (cm) 60 2.0-6.0 3.26 + 0.85 Infructescence stalk diameter (mm) 60 7 O2350 2.54 + 0.33 Fruit stalk length (cm) 60 O6=TZ 1.03 + 0.25 Fruit stalk diameter (mm) 60 3.0-5.0 3.66 + 0.39 Hypocotyl length (cm) As: 19.5-40.0 30.01 + 3.25 Hypocotyl diameter at the apical part (mm) 25 6.5-9.0 7.64 + 0.65 Hypocotyl diameter at the widest part (cm) Bas 1016 1.29 +0.12 Hypocotyl diameter at the basal part (cm) 75 0.8-1.3 0.99 + 0.10 Cotyledonous tube diameter (cm) 75 0.6=132 0.86 +0.14 PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Distribution in Thailand. Rhizophora stylosa is known only from Ko Lidi and Ko Bulon Le within Mu Ko Phetra National Park, located in La-ngu District, and from Ao Talo Wao, Ko Tarutao, in Tarutao National Park, Mueang Satun District, Satun Province, Peninsular Thailand (Fig. 6). Habitat and ecology. Rhizophora stylosa typically occurs along coastal areas with muddy-sandy, sandy or sandy-rocky substrates. This species is found at the seaward edge of mangrove forests and is well adapted to grow in open coastal environments, particularly along fairly exposed shores. The populations of R. stylosa observed in Thailand are also located in low intertidal zones characterized by rocky and sandy substrates, similar to the ob- servations reported from the Andaman and Nicobar Islands, India by Ragavan (2015) and Ragavan et al. (2021). In the Andaman and Nicobar Islands, the species is uncommon and is most- ly found in mangroves fringing the open coast, towards the seaward side. It is often found in mid to low intertidal zones and along downstream tidal creeks. The species grows in a variety of habitats, including disturbed mangrove areas. One distinctive niche is its ability to grow along the edges of small coral islands, where it establishes on coral substrates (Ragavan 2015; Ragavan et al. 2021). Phenology. Flowering, fruiting and viviparous germination more than once, nearly throughout the year. Conservation status. Rhizophora stylosa is widely distributed, ranging from India (Andaman and Nicobar Islands) and China through Indo-China to the Pacific Islands. It is known from numerous localities, with a very large EOO of 52,723,897.41 km? and a relatively large AOO of 1,908 km2. In Thailand, however, the species is restricted to Satun Province in the peninsular region, where it has a small EOO of 251.22 km? and a relatively small AOO of 12 km?. Despite its lim- ited national distribution, its broad global range, presence in numerous localities, and the absence of significant threats to its survival, we recommend a conserva- tion assessment of Least Concern (LC), in agreement with Ellison et al. (2010). Etymology. The specific epithet of Rhizophora stylosa is a Latin word that refers to its characteristic long style. Vernacular name. Kongkang phetra (insmanaz1) (Suggested here); Red man- grove, Small stilted mangrove, Spotted mangrove, Stilted mangrove (English). Uses. To date, there has been no record of its use in Thailand. On Japan's Irio- mote Islands, the traditional dyeing of cotton fabric using tannins extracted from the bark of Rhizophora stylosa (Yaeyama hirugi), a technique known as kusa- ki-zome, remains an important cottage industry. The dye from the outer bark is brownish, while that from the inner bark is reddish (Baba 2004; Baba et al. 2013). On Iriomote and Ishigaki Islands, seedlings of R. stylosa are sold in souvenir shops to tourists as ornamentals (Baba et al. 2013). This species is utilized for timber, firewood, and the production of charcoal in the Pacific Island countries (Giesen et al. 2007; Kainuma et al. 2015). In Australia, Aboriginal people use its wood to make boomerangs, spears, and ceremonial items (Giesen et al. 2007). Lectotypification. Rhizophora stylosa was named by Griffith (1854: 665), who cited only the type locality “Hab. Malacca, in littoribus limosis, Pulo Bissar”. How- ever, he did not designate a holotype, nor did he provide a collector number or in- dicate the herbarium where the material was housed. We have located the speci- men W. Griffth s.n. from Malacca at K [K005752944] and BR[BR0000031831338], which following Art. 9.6 of the ICN (Turland et al. 2018), must be considered syn- PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 12 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand types. William Griffith (1810-1845) was a British colonial physician and botanist who made substantial contributions to the herbarium of the East India Compa- ny. His herbarium was originally deposited at LINN, but was later transferred to Kew (kK), with significant duplicate specimens housed at BR and CAL (Stafleu and Cowan 1976). Accordingly, we designate the specimen at K [K005752944] as the lectotype, with the specimen at BR [BRO000031831338] being an isolec- totype, in accordance with Arts. 9.3 and 9.12 of the ICN (Turland et al. 2018). Notes. The colors and sizes of the stipules of Rhizophora stylosa are pale green or green, turning whitish pale green or creamish white before falling off. They are 3.5-7.5 cm long, 2.5-9 mm diam. at the base. In contrast, the stipules of R. mucronata are pale green, reddish pale green, or pale greenish red when young, turning pale yellow or reddish pale yellow before falling off, and are larg- er, 4.5-12.5 cm in length and 0.5-1.7 cm in diameter at the base. The petioles, peduncles, rachises of inflorescences, and pedicels of R. stylosa are usually terete, whereas those of R. mucronata are slightly to somewhat flattened. Morphologically, R. stylosa is closely related to R. mucronata (Fig. 7) in its in- florescences and flowers (including flower buds, pedicelled flowers, bracteoles, sepals, and stamens); in the length of the stiff, pointed leaf tips; in the shape and basal diameter of the fruits (when the hypocotyls nearly come off); in the shape and color of the hypocotyls; and in the colors of the cotyledonous cylin- drical tubes and colleters. The differences between these two Thai species of Rhizophora are presented in Table 2. Two distinct populations of R. stylosa were found in Mu Ko Phetra Nation- al Park, La-ngu District, Satun Province, Peninsular Thailand. Population A is distributed along coastal areas characterized by muddy-sandy substrates, pre- dominantly occupying the seaward edge of the mangrove forest at Ko Lidi, La- ngu Subdistrict. In contrast, Population B occurs along coastal areas with san- dy to sandy-rocky substrates, particularly along relatively exposed shorelines at Ko Bulon Le, Pak Nam Subdistrict. Morphological comparisons between the two populations reveal that individuals in Population A (3-8 m) tend to be taller than those in Population B (2.5—5 m). Furthermore, vegetative and reproductive Table 2. Morphological differences between Rhizophora stylosa and R. mucronata in Thailand. The morphological char- acteristics of R. mucronata are based on Ngernsaengsaruay et al. (2024). Morphological characters Rhizophora stylosa Habit Small trees, single- to multi-stemmed, 2.5-8 m tall Stipule colours and sizes Pale green or green, turning whitish pale green or creamish white before the leaves emerging or before falling off, smaller, 3.5-7.5 cm long and 2.5-9 mm diam at the base Elliptic, smaller, 8-16 x 3-8.5 cm, widest at the middle part Narrowly elliptic or elliptic, densely and longer villous along margins Shorter, 0.7-1.2 mm long 3-5 mm long Smaller, 2-2.7 cm long, 1-1.7 cm diam. at the Leaf shapes and sizes Petal shapes and hairs Free part of the ovary length Style length Fruit sizes (ovoid or conical- ovoid, before seed germination) basal part Fruit sizes (obpyriform, when Smaller, 2.2-4 cm long, 1.7-3 cm diam. at the the hypocotyls nearly come off) basal part Hypocotyl length Shorter, 19.5-40 cm long PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 Rhizophora mucronata Small to large trees, 2-20 (—30) m tall, usually single- stemmed Pale green, reddish pale green or pale greenish red when young, turning pale yellow or reddish pale yellow before the leaves emerging or before falling off, larger, 4.5-12.5 cm long, 0.5-1.7 cm diam at the base Ovate or lanceolate-ovate, larger, 13-23.5 x 6-13 cm, widest at the basal part Lanceolate-ovate or lanceolate, densely and shorter villous along margins Longer, 1.5-3 mm long Very short Larger, 3.7-5 cm long, 2.1-2.8 cm diam. at the basal part Larger, 4-7 cm long, 2.4—3.5 cm diam. at the basal part Longer, 25-70 cm long Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Figure 7. Rhizophora mucronata. A. Branchlets, leaves and terminal interpetiolar stipule; B. Leaves showing adaxial and abaxial surfaces; C. Flowering branchlet showing inflorescences with flower buds and fully open flower; D. Petal with densely and shorter villous along margins; E. Flower bud in longitudinal section showing very short style; F. Fruiting branchlet showing leaves and mature fruit with persistent sepals; G, H. Fruiting branchlets showing leaves and succes- sive stages in development of hypocotyl. Photos: Chatchai Ngernsaengsaruay (A-C, F-H), Pichet Chonton (D, E). PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 14 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Table 3. Comparison of the morphological characteristics between two populations of Rhizophora stylosa in Mu Ko Phetra National Park, La-ngu District, Satun Province, Thailand. Population A occurs along coastal areas with muddy-sandy sub- strates, particularly at the seaward edge of mangrove forest at Ko Lidi, La-ngu Subdistrict. Population B occurs along coast- al areas with sandy or sandy-rocky substrates, especially along fairly exposed shores at Ko Bulon Le, Pak Nam Subdistrict. : ; Sample Rhizophora stylosa Population A | Rhizophora stylosa Population B Morphological characters (units) : sizes Ranges Mean + SD Ranges Mean + SD Stipule length (cm) A 30/B 50 4.0-7.5 5.78 + 1.03 3.5-6.5 5.16+0.77 Stipule diameter at the base (mm) A 30/B 50 3.0-9.0 5.06 + 2.04 2.57360 3.68 + 0.91 Leaf lamina length (cm) 150 9.5-16.0 12:92 P10 8.0-12:.5 10.14+0.94 Leaf lamina width (cm) 150 4.5-8.5 6.01 + 0.76 320-920 4.39 + 0.44 Petiole length (cm) 150 2.5-4.8 3.63 + 0.44 2.0-4.0 2.88 + 0.36 Petiole diameter at the middle (mm) 150 225545 3.45 + 0.38 20-35 2:93 +'0.3:1 Inflorescence length (cm) 90 6:0-12.5 8.80 + 1.18 5.0-9.0 7.05 + 0.87 Peduncle length (cm) 90 2.8-6.0 4.39 + 0.65 234-0 3.22 + 0.49 Fruit length (cm) (hypocotyls nearly come off) | A 20/B 50 3.0-4.0 3.49 + 0.31 2°2-330 2.68 + 0.17 Fruit diameter at the basal part (cm) A 20/B 50 1.9-3.0 2.25 + 0.31 7-23 1.95+0.11 structures, including stipules, leaves, petioles, inflorescences, peduncles, and fruits, are generally larger in Population A. These morphological differences are likely influenced by environmental conditions, suggesting that substrate type and coastal exposure play significant roles in shaping the growth and reproduc- tive traits of R. stylosa in this region (Table 3). Additional specimens examined. THAILAND. Peninsular: * Satun [Ko Lidi, Mu Ko Phetra National Park, La-ngu Subdistrict, La-ngu District, fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. Rs01-22042025 (BKF); * Ao Phangka, Ko Bulon Le, Mu Ko Phetra National Park, Pak Nam Subdistrict, La-ngu District, fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. Rs02-22042025 (BKF); - ibid., fl., fr. & vivipary, 22 Apr 2025, C. Ngernsaengsaruay et al. RS03-22042025 (BKF); Ao Talo Wao, Ko Tarutao, Tarutao National Park, Mueang Satun District, fl., 30 May 2025, N. Mianmit & N. Kaveethanathum personal observation with photos; Note. C. Ngernsaengsaruay et al. = C. Ngernsaengsaruay, N. Mianmit, R. Pothitan, V. Jintana, N. Jintana & S. Kamsanor). A key to the species of Rhizophora in Thailand (Modified from Ngernsaengsaruay et al. 2024) 1 Inflorescences on leafless branchlets (in the axils of leaf scars), 2-flow- ered cymes; flowers sessile; flower buds pale green, usually tinged with brown, finely reticulated, broadly ellipsoid or ellipsoid; bracteoles brown, connate, cup-shaped, shallowly lobed; sepals elliptic-oblong, thickly cori- aceous; petals flattened, not involute, glabrous; stamens mostly 12; fruits up to 1.8 cm diam. at the basal part (when the hypocotyls nearly come off); hypocotyls dark green or purplish dark green; cotyledonous cylindrical tubes red, dark greenish red or reddish dark green; stipules bearing bright yellow colleters that produce a sticky, clear exudate; the stiff, pointed tips of the leaves usually less than 3 mm long.................. Rhizophora apiculata - Inflorescences axillary, dichotomously branched, many-flowered cymes; flowers pedicelled; flower buds pale green, turning pale yellow when ma- PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 15 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand ture, ovoid or conical-ovoid; bracteoles pale green, connate at the base, bilobed; sepals triangular, coriaceous; petals involute, villous along mar- gins; stamens 8; fruits usually more than 1.8 cm diam. at the basal part (when the hypocotyls nearly come off); hypocotyls green; cotyledonous cylindrical tubes pale green or greenish pale yellow; stipules bearing pale yellow colleters that produce a sticky, white exudate; the stiff, pointed tips of the leaves usually more than 3 MM lONG...........c:cccscccesssccsseeeesseeeseeeseees 2 2 Leaves ovate or lanceolate-ovate, larger, 13-23.5 x 6-13 cm; petals lanceo- late-ovate or lanceolate, densely and shorter villous along margins; free part of the ovaries, longer, 1.5-3 mm long; style very short; fruits (before seed germination) larger, 3.7—5 cm long, 2.1-2.8 cm diam. at the basal part; fruit (when the hypocotyls nearly come off) larger, 4-7 cm long, 2.4-3.5 cm diam. at the basal part; hypocotyls longer, 25-70 cm long; small to large trees, 2-20 (-30) m tall, usually single-stemmed.................. Rhizophora mucronata - Leaves elliptic, smaller, 8-16 x 3-8.5 cm; petals narrowly elliptic or el- liptic, densely and longer villous along margins; free part of the ovaries, shorter, 0.7—1.2 mm long; style 3-5 mm long; fruits (before seed germina- tion) smaller, 2-2.7 cm long, 1-1.7 cm diam. at the basal part; fruit (when the hypocotyls nearly come off) smaller, 2.2—4 cm long, 1.7—-3 cm diam. at the basal part; hypocotyls shorter, 19.5-40 cm long; small trees, single- to miulti-stemmed, 2: 558210 tall ..ccccccssceesenessvereceeccasecrgessanves Rhizophora stylosa Anatomical study Leaf anatomy of Rhizophora stylosa in Thailand The leaf anatomical structure of Rhizophora stylosa is composed of five principal tissue layers: adaxial epidermis, hypodermis, palisade mesophyll, spongy meso- phyll, and abaxial epidermis. Leaf thickness ranges from 574.11-881.72 um. A thick cuticular wax layer (cuticle) covers both epidermal surfaces, with the adax- ial surface bearing a slightly thicker cuticle than the abaxial surface (Fig. 9). Epidermal cells are polygonal, occasionally trapezoidal with straight anticlinal walls, and are arranged in a single layer on both adaxial and abaxial surfaces. The adaxial epidermis is slightly thicker than the abaxial epidermis (Fig. 8). The stomata of R. stylosa are confined to the abaxial leaf surface, indicating that the leaves are hypostomatic. The stomata are of the sunken cyclocytic type, surrounded by 6-8 subsidiary cells arranged in a concentric ring around each stoma (Fig. 8). Stomatal size rang- es from 18.31-30.48 x 9.56-15.21 um, with a density of 77-153 stomata/mm~. According to previous studies, stomatal density is categorized into three groups: low (<300 stomata/mm7), medium (300-500 stomata/mm7?), and high (>500 stomata/mm?). Based on this classification, the stomatal density of R. stylosa is considered low. Cork warts are present on the abaxial surface, with a density ranging from 15-52 cork warts percm? and a diameter of 41.57-—94.58 um. These structures consist of densely packed cells, morphologically distinct from other epidermal cells and easily distinguishable from stoma (Fig. 8). Rhizophora stylosa has the largest cork wart size among the three species in Thailand. Rhizo- phora mucronata exhibits cork wart sizes ranging from 39.86-82.36 ym, with an average of 61.76 + 12.83 um, while R. apiculata has the smallest cork wart sizes, PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 16 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand 50 ym __ 100 ym — Sci. Equip. Center KU Figure 8. Leaf anatomy of Rhizophora stylosa. A. Adaxial epidermis (under LM); B, C. Abaxial epidermis (under LM); D. Abaxial epidermis (under SEM) (Cw = cork wart, EpC = epidermal cells, St = stoma, and SubC = subsidiary cells). Photos: Pichet Chanton & Chatchai Ngernsaengsaruay. ranging from 35.69-75.48 um, with an average of 54.99 + 10.64 um. The data for R. apiculata and R. mucronata are based on Ngernsaengsaruay et al. (2024). Rhizophora stylosa possesses bifacial leaves. The mesophyll is composed three main tissues: hypodermis, palisade parenchyma, and spongy parenchy- ma (Fig. 9). The hypodermis consists of relatively large cells arranged in multi- ple layers beneath the epidermis. These cells are often filled with tannins, which cause them to appear darkly stained. The adaxial surface exhibits a greater average hypodermal thickness compared to the abaxial surface. Hypodermal cells on the adaxial side are typically subcircular, elliptic, ob- long, or rounded polygonal in shape, while those on the abaxial side tend to be broadly elliptic, circular, or rounded polygonal. The average cell size of the hypo- dermis is also larger on the adaxial surface than on the abaxial surface (Fig. 9). Druse crystals are present in the hypodermal cells on both the adaxial and abaxial surfaces. The diameter of the druse crystals ranges from 14.84- 30.06 ym (Fig. 9). PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 7 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand The palisade parenchyma consists of one to two layers of tightly packed, elongated cells located directly beneath the hypodermis. The spongy parenchy- ma is composed of five to seven layers of loosely arranged, irregularly shaped cells situated below the palisade parenchyma and above the abaxial epidermis. This tissue exhibits prominent intercellular spaces, forming a characteristic net-like structure (Fig. 9). mis, Cr = druse crystals, Ct = cuticle, Cw = cork wart, EpC = epidermal cells, Hp = hypodermis, P = phloem, Pa = paren- chyma, PI = palisade mesophyll, Sp = spongy mesophyll, St = stoma, Vb = vascular bundle, X = xylem). Photos: Pichet Chanton & Chatchai Ngernsaengsaruay. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 18 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Observations of the vascular bundle arrangement in the midrib of R. stylosa reveal a complex structure, divided into three distinct regions: abaxial, medul- lary (central), and adaxial. Each vascular bundle comprises phloem located on the outer side and xylem on the inner side. These vascular bundles are incom- pletely enclosed by a layer of sclerenchyma cells (Fig. 9). A comparison of the leaf anatomical characteristics of R. stylosa in Thailand with findings from previous studies is presented in Table 4. Table 4. Comparison of the leaf anatomical characteristics of Rhizophora stylosa in Thailand with previous studies from other countries: "!Sheue (2003), “Evans et al. (2008), and ®!Putri and Bashri (2023). Anatomical characters From the author's observations Previous studies Leaf thickness (um) 574.11-881.72 (720.53 + 92.18,n=20) | 571.5 + 21.3 (Australia) 556.0 + 31.4 (Singapore)! Leaf structure type Bifacial leaves Dorsiventral leaves" (= bifacial leaves) Cuticular wax thickness on the adaxial leaf surface (um) 14.13-34.65 (25.46 + 5.85, n = 20) 7.04 + 1.94" Cuticular wax thickness on the abaxial leaf surface (um) 13.27-33.38 (23.80 + 6.93, n = 20) 5.25 + 1.23! Number of epidermal cell layer on the adaxial leaf surface 1-layered 1-layered" Number of epidermal cell layer on the abaxial leaf surface 1-layered 1-layered!"! Epidermal layer thickness on the adaxial leaf surface (um) 20.40-43.55 (26.97 + 5.78, n = 20) 7 Epidermal layer thickness on the abaxial leaf surface (um) 17.25-37.31 (30.05 + 5.96, n = 20) = Epidermal cell shapes on the adaxial leaf surface Polygonal, sometimes trapezium Polygonal, 29-35 x 17-25 pm © Epidermal cell shapes on the abaxial leaf surface Polygonal, sometimes trapezium Polygonall*! Stomatal types Sunken cyclocytic Cyclocytic!, Stomatal density per mm? 77-153 (108.91 + 18.19, n = 100) 61.15 (mean), low density, 9-12 (number of stomata in one field of view, 400x magnification)®! Stomatal length (um) 18.31-30.48 (24.65 + 3.42, n = 100) 49.50 + 2.70", Stomatal width (um) 9.56-15.21 (12.20 + 1.61, n = 100) 43.27 + 2.27", Stomatal length/width ratio 1.39-3.19 (2.05 + 0.41, n = 100) 1.14! Number of subsidiary cells 6-8 (6.84 + 0.81, n = 50) (5-)6-74 Cork wart density per cm? 15-52 (31.60 + 9.85, n = 300) 10.1 + 0.4 (mm?) Cork wart density at the apical part per cm? 30-52 (41.92 + 6.11, n = 100) = Cork wart density at the middle part per cm? 24-40 (31.30 + 4.88, n = 100) = Cork wart density at the basal part per cm? 15-28 (21.33 + 4.07, n = 100) = Cork wart diameter (um) 41.57-94.58 (67.29 + 15.69, n = 100) 196.00 + 20.86 (Singapore)! Hypodermal layer thickness on the adaxial leaf surface (um) | 206.41-361.11 (260.49 + 43.90, n = 20) Hypodermal layer thickness on the abaxial leaf surface (um) | 50.67-110.54 (80.36 + 18.41, n = 20) 252.00 + 46.11 (Taiwan)! Number of hypodermal cell layer on the adaxial leaf surface 4-6-layered (5.25 + 0.72, n = 20) 2-layered (small-sized) and 3-layered (large-sized), 5- layered! Number of hypodermal cell layer on the abaxial leaf surface 2-3-layered (2.45 + 0.51, n = 20) 1(-3)-layered"”! Hypodermal cell shapes on the adaxial leaf surface (um) Subcircular, elliptic, oblong or rounded Rounded hexagon ©! polygonal Hypodermal cell length on the adaxial leaf surface (um) 31.90-99.67 (73.12 + 20.65, n = 20) 49-738) Hypodermal cell width on the adaxial leaf surface (um) 29.69-73.84 (53.55 + 12.55, n = 20) 34-46" Hypodermal cell shapes on the abaxial leaf surface (um) Broadly elliptic, circular or rounded = polygonal Hypodermal cell length on the abaxial leaf surface (um) 18.78-47.27 (33.53 + 6.92, n = 20) = Hypodermal cell width on the abaxial leaf surface (um) 19.61-46.08 (31.32 + 6.21, n = 20) = Crystal location, type and diameter (um) Druse (in hypodermal cells), 14.84— = 30.06 (22.62 + 3.98, n = 20) Number of palisade cell layer 1-2-layered (1.40 + 0.50, n = 20) 1—-4-layered (upper), 0-1-layered (lower)! Number of spongy cell layer 5-7-layered (6.05 + 0.76, n = 20) 9-10-layered (Australia), PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 7-8-layered (Singapore)! Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Palynological study Pollen morphology of Rhizophora stylosa in Thailand The pollen grains of Rhizophora stylosa are monads, isopolar, radially symmet- rical, and tricolporate. They exhibit either a prolate spheroidal or oblate sphe- roidal shape, with a P/E ratio ranging from 0.88-1.15. In polar view (amb), the outline is subcircular or rounded triangular. The pollen grains are small in size, with the polar axis measuring 17.93- 22.36 um and the equatorial axis 16.79-22.94 um. The colpus length ranges from 12.92-20.40 um, and the colpus width from 2.35-3.85 um. The exine thickness ranges from 0.83-2.43 um., and the exine sculpturing is reticu- late (Fig. 10). Rhizophora stylosa has the largest pollen size among the three A 20 um B 20 ym 5/15/2025 | HV |mag | HFW | WD |mode|.—t1u~m—— 7:25:34 PM |20.00 kV| 30 000 x/4.97 um|8.0 mm| SE Sci. Equip. Center KU Figure 10. LM and SEM micrographs of pollen grains of Rhizophora stylosa. A. Tricolporate aperture and rounded-trian- gular shape in polar view; B. Colporate aperture in equatorial view; C. Tricolporate aperture and rounded-triangular shape in polar view; D. Colporate aperture in equatorial view; E. Exine sculpturing, under LM (A, B), under SEM (C-E). Photos: Pichet Chanton & Chatchai Ngernsaengsaruay. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 20 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand species in Thailand. Rhizophora mucronata exhibits pollen sizes along the polar axis ranging from 12.37-18.49 um, with an average of 15.77 + 1.58 um, while R. apiculata has the smallest pollen size along the polar axis, ranging from 11.16-13.50 um, with an average of 12.36 + 0.78 um. The data for R. apiculata and R. mucronata are based on Ngernsaengsaruay et al. (2024). A comparison of the pollen morphology of Rhizophora stylosa in Thailand with previous studies is presented in Table 5. Table 5. Comparison of the pollen morphology of Rhizophora stylosa in Thailand with previous studies from other coun- tries: "Mao et al. (2012) and "IMohd-Arrabé and Noraini (2013). Pollen characters From the author's observations Previous studies Polar axis [P] length (um) 17.93-22.36 (20.59 + 1.35,n=30) | 19.9 (20.5) 22.7 x 21.3 (22.4) 24.7". 17.29 (19.17) 21.2721 Equatorial axis [E] length (um) | 16.79-22.94 (20.08 + 1.64, n = 30) 16.61 (18.62) 20.462 P/E ratio 0.88-1.15 (1.03 + 0.07, n = 30) 1.031 Pollen size classes Small = Pollen shapes Prolate spheroidal or oblate spheroidal Subprolate, circular to subcircular!:; prolate-speroidal!# Pollen aperture Tricolporate Tricolporate!™ 2) Colpus length (um) 12.92-20.40 (16.48 + 2.15, n = 30) 13.411 Colpus width (um) 2:35=3:85 (3.21, +:0.37,n= 30) = Exine thickness (um) 0.83-2.43 (1.54 + 0.39, n = 30) 1.5! 0.79 (0.95) 1.2421 Exine sculpturing Reticulate Scabrate to slightly granulate to irregularly pitted", perforate?! Acknowledgements We express our sincere gratitude to the curators and staff of the BK and BKF her- baria for their assistance during our visits and for facilitating access to the herbar- ium specimens. We also extend our thanks to the institutions maintaining virtual herbarium databases, including A, BR, CAL, E, K, L, PR SING, and US, as well as to the Global Biodiversity Information Facility (GBIF, https://www.gbif.org/), which provid- ed access to valuable specimen data. Special thanks are extended to Wanwisa Bhuchaisri for the line drawing. We are also grateful to Kullanis Nakwichian, Sinsu- pa Jongkrajak, Jutamad Srikongruk, the staff of Mu Ko Phetra National Park and Nakain Kaveethanathum, Assistant Chief of Tarutao National Park, for their kind as- sistance with fieldwork. We further wish to thank Weereesa Boonthasak, Wimolsiri Sriwijainun, and Kamutphon Numuean for their valuable support in the laboratory. Additional information Conflict of interest The authors have declared that no competing interests exist. Ethical statement No ethical statement was reported. Funding This study was funded by Kasetsart University from research funding through the Biodi- versity Center Kasetsart University (BCKU) and the International SciKU Branding (ISB), Faculty of Science, Kasetsart University. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 71 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Author contributions Conceptualization: CN, NM. Data curation: CN, PC. Formal analysis: CN, NM. Funding acquisition: CN. Investigation: CN, NM, RP VJ, NJ, SK, JK. Methodology: CN, NM, PC. Project administration: CN, NM, SK. Resources: CN, NM, PC, AK, SK. Writing — original draft: CN, NM. Writing — review and editing: CN, NM, RP, VJ, NJ, SK, PC. Author ORCIDs Chatchai Ngernsaengsaruay ® https://orcid.org/0000-0002-7131-976X Nittaya Mianmit © https://orcid.org/0000-0002-1295-8078 Vipak Jintana © https://orcid.org/0000-0002-7703-7288 Pichet Chanton © https://orcid.org/0009-0001-7325-6109 Data availability All of the data that support the findings of this study are available in the main text. References Baba S (2004) Keynote Presentation: What we can do for mangroves. In: Vannucci M (Ed.) Mangrove Management and Conservation: Present and Future. United Nations University Press, Tokyo, Japan, 8-36. Baba S, Chan HT, Aksornkoae S (2013) Useful Products from Mangrove and Other Coastal Plants. ISME Mangrove Educational Book Series No. 3. International Society for Mangrove Ecosystems (ISME), Okinawa, Japan, and International Tropical Timber Organization (ITTO), Yokohama, Japan, 98 pp. Bachman S, Moat J, Hill AW, de la Torre J, Scott B (2011) Supporting red list threat assessments with GeoCAT: Geospatial conservation assessment tool. In: Smith V, Penev L (Eds) e-Infrastructures for data publishing in biodiversity Science. ZooKeys 150: 117-126. https://doi.org/10.3897/zookeys.150.2109 Backer CA, Bakhuizen van den Brink RC (1963) Rhizophoraceae. In: Flora of Java Vol 1. N. V. P. Noordhoff, Groningen, The Netherlands, 378-381. Duke NC (2010) Overlap of eastern and western mangroves in the south-western Pacific: Hybridization of all three Rhizophora (Rhizophoraceae) combinations in New Caledo- nia. Blumea 55(2): 171-188. https://doi.org/10.3767/000651910X527293 Duke NC, Bunt JS (1979) The genus Rhizophora (Rhizophoraceae) in North-eastern Austra- lia. Australian Journal of Botany 27(5): 657-678. https://doi.org/10.1071/BT9790657 Ellison J, Duke N, Kathiresan K, Salmo Ill SG, Fernando ES, Peras JR, Sukardjo S, Miyagi T (2010) Rhizophora stylosa. The IUCN Red List of Threatened Species 2010. https://doi. org/10.2305/IUCN.UK.2010-2.RLTS.T178850A7626520.en [Accessed on 24 April 2025] Erdtman G (1945) Pollen morphology and plant taxonomy V. on the occurrence of tet- rads and dyads. Svensk Botanisk Tidskrift Utgifven af Svenska Botaniska Foreningen 39: 286-297. Erdtman G (1952) Pollen Morphology and Plant Taxonomy: Angiosperms Vol 1. Alm- quist and Wiksell, Stockholm, 539 pp. Evans LS, de Leon MF, Sai E (2008) Anatomy and morphology of Rhizophora stylosa in relation to internal airflow and Attim’s plant architecture. The Journal of the Torrey Botanical Society 135(1): 114-125. https://doi.org/10.3159/07-RA-027R.1 Giesen W, Wulfraat S, Zieren M, Scholten L (2007) Mangrove Guidebook for Southeast Asia. FAO, Bangkok, Thailand and Wetlands International, Wageningen, Netherlands, 235=239. PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 99 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Griffith W (1854) Notulae Ad Plantas Asiaticas: Dicotyledonous Plants Vol 4. John M'Clelland, F. L. S., Calcutta, 662-671. Henslow G (1878) Rhizophoreae. In: Hooker JD (Ed.) The Flora of British India Vol 2. L. Reeve & Co., London, 434-443. Hou D (1958) Rhizophoraceae. In: van Steenis CGGJ (Ed.) Flora Malesiana Series 1, Vol 5. Noordhofef-Kolff N. V., Jakarta [Djakarta], 429-493. Hou D (1960) A review of the genus Rhizophora with special reference to the Pacific species. Blumea 10(2): 625-634. Hou D (1970) Rhizophoraceae. In: Smitinand T, Larsen K (Eds) Flora of Thailand Vol 2. The Forest Herbarium, Bangkok, 5-15. IPNI (2025) International plant names index. The Royal Botanic Gardens, Kew, Harvard University Herbaria & Libraries and Australian National Herbarium. http://www.ipni.org IUCN Standards and Petitions Committee (2024) Guidelines for Using the IUCN Red List Categories and Criteria Version 16. Standards and Petitions Committee. https:// www.iucnredlist.org/resources/redlistguidelines Johansen DA (1940) Plant Microtechnique. McGraw-Hill, New York, 523 pp. Kainuma M, Kezuka M, Inoue T, Chan EWC, Tangah J, Baba S, Chan HT (2015) Botany, uses, chemistry and bioactivities of mangrove plants |: Rhizophora stylosa. ISME/ GLOMIS Electronic Journal 13(4): 12-17. Kannan S, Ragavan P. Gopalakrishan K, Salah M, Balasubramani K (2021) Mangrove floris- tics, forest structure and mapping of Neil Island (Andaman and Nicobar Islands, India) with emphasis on the diversity of Rhizophora species and the significance of small island mangroves. Botanica Marina 64(3): 227-241. https://doi.org/10.1515/bot-2020-0075 Kermanee P (2008) Techniques of Plant Tissues. Kasetsart University, Bangkok, 289 pp. [in Thai] King G (1897) Materials for A Flora of The Malayan Peninsula (Rhizophoreae). Journal Asiatic Society of Bengal Part 2(1): 311-326. Mao L, Batten DJ, Fujiki T, Li Z, Dai L, Weng C (2012) Key to mangrove pollen and spores of southern China: An aid to palynological interpretation of Quaternary deposits in the South China Sea. Review of Palaeobotany and Palynology 176-177: 41-67. https:// doi.org/10.1016/j.revpalbo.2012.03.004 Marchand M (2008) Mangrove Restoration in Vietnam: Key Considerations and A Prac- tical Guide. Report Prepared for WRU, TUD, Deltares, Delft. McCusker A (1984) Rhizophoraceae. In: Briggs BG, Barlow BA, Eichler H, Pedley L, Ross JH, Symon DE, Wilson PG (Eds) Flora of Australia Vol 22. Griffen Press Ltd., South Australia, 1-10. Metcalfe CR, Chalk L (1957) Anatomy of the Dicotyledons: Leaves, Stem, and Wood in Relation to Taxonomy, with Notes on Economic Uses. Vol 1. Oxford University Press, Oxford, 1459 pp. Mohd-Arrabé AB, Noraini T (2013) Pollen morphology of Rhizophora L. in Peninsular Malay- sia. AIP Conference Proceedings 1571: 377-381. https://doi.org/10.1063/1.4858687 Ng WL, Chan HT (2012) Further observations on a natural Rhizophora hybrid population in Malaysia. ISME/GLOMIS Electronic Journal 10(1): 1-3. Ng WL, Chan HT, Szmid AE (2013) Molecular identification of natural mangrove hybrids of Rhizophora in Peninsular Malaysia. Tree Genetics & Genomes 9(5): 1151-1160. https://doi.org/10.1007/s11295-013-0619-7 Ngernsaengsaruay C, Chanton P Leksungnoen N, Uthairatsamee S, Mianmit N (2024) A taxonomic revision of Rhizophora L. (Rhizophoraceae) in Thailand. PeerJ 12(e17460): 1-46. https://doi.org/10.7717/peerj.17460 PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 93 Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand Parani M, Rao CS, Mathan N, Anuratha CS, Narayanan KK, Parida A (1997) Molecu- lar phylogeny of mangroves III parentage analysis of a Rhizophora hybrid using random amplified polymorphic DNA and restriction fragment length polymor- phism markers. Aquatic Botany 58(2): 165-172. https://doi.org/10.1016/S0304- 3770(97)00003-X POWO (2025) Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. http://www.plantsoftheworldonline.org/ Putri RY, Bashri A (2023) Anatomical characteristics of Rhizophora’s leaves as mangrove plant adaptation at Banyuurip Mangrove Center. Jurnal Riset Biologi dan Aplikasinya 5(2): 98-109. https://doi.org/10.26740/jrba.v5n2.p98-109 Punt W, Hoen PP, Blackmore S, Nilsson S, Thomas AL (2007) Glossary of pollen and spore terminology. Review of Palaeobotany and Palynology 143(1-2): 1-81. https:// doi.org/10.1016/j.revpalbo.2006.06.008 Qin H, Boufford DE (2007) Rhizophoraceae. In: Wu CY, Raven PH, Hong DY (Eds) Flora of China Vol 13. Science Press, Beijing, Missouri Botanical Garden Press, St. Louis, 295-299. Ragavan P (2015) Taxonomy of Mangroves of the Andaman and Nicobar Islands with Special Reference to Natural Hybrids of Genus Rhizophora. PhD Thesis, Pondicherry University (A Central University), Brookshabad Campus, Andaman, India, 422 pp. Ragavan P, Jayaraj RSC, Saxena A, Mohan PM, Ravichandran K (2015) Taxonomical identity of Rhizophora x annamalayana Kathir and Rhizophora x lamarckii Montrouz (Rhizophoraceae) in the Andaman and Nicobar Islands, India. Taiwania 60(4): 183- 193. https://doi.org/10.6165/tai.2015.60.183 Ragavan P, Kathiresan K, Rana TS, Saxena A, Mohan PM, Jayaraj RSC, Ravichandran K, Mageswaran T (2021) Indian Mangroves: A Photographic Field Identification Guide. New India Publishing Agency, India, 207 pp. https://doi.org/10.59317/97893901 75994 Ridley HN (1922) Rhizophoraceae. In: The Flora of the Malay Peninsula Vol 1. L. Reeve & Co. Ltd., London, 692-696. https://doi.org/10.5962/bhi.title.10921 Schwarzbach AE (2014) Rhizophoraceae. In: Kubitzki K (Ed.) The Families and Genera of Vascular Plants Vol 11. Springer-Verlag, Berlin/Heidelberg, 283-295. https://doi. org/10.1007/978-3-642-3941 7-1_23 Setyawan AD, Ulumuddin YI, Ragavan P (2014) Review: Mangrove hybrid of Rhizophora and its parental species in Indo-Malayan region. Nusantara Bioscience 6(1): 67-79. https://doi.org/10.13057/nusbiosci/n060111 Sheue CR (2003) The Comparative Morphology and Anatomy of the Eastern Mangrove Rhizophoraceae. Ph.D. Dissertation. National Sun Yat-sen University, Kaohsiung, Taiwan. Sheue CR, Chen YJ, Yang YP (2012) Stipules and colleters of the mangrove Rhizophora- ceae: Morphology, structure and comparative significance. Botanical Studies 53(2): 243-254. Simpson MG (2010) Plant Systematics. 2" edn., Elsevier Academic Press, Burlington/ San Diego, 740 pp. Stafleu FA, Cowan RS (1976) Taxonomic Literature: A Selective Guide to Botanical Pub- lications and Collections with Dates, Commentaries and Types Vol 1 [A-G]. 2"! edn., Bohn, Scheltema & Holkema, Utrecht. https://doi.org/10.5962/bhI.title.48631 Stafleu FA, Cowan RS (1983) Taxonomic Literature: A Selective Guide to Botani- cal Publications and Collections with Dates, Commentaries and Types Vol 4 [P- Sak]. 2"! edn., Bohn, Scheltema & Holkema, Utrecht, The Netherlands. https://doi. org/10.5962/t.206493 PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 oA Chatchai Ngernsaengsaruay et al.: Rhizophora stylosa in Thailand The Angiosperm Phylogeny Group (2016) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society 181: 1-20. https://doi.org/10.1111/boj.12385 Thiers B (2025) [continuously updated] Index Herbariorum: A Global Directory of Pub- lic Herbaria and Associated Staff. New York Botanical Garden's Virtual Herbarium. http://sweetgum.nybg.org/science/ih/ Tomlinson PB (1978) Rhizophora in Australasia. Journal of the Arnold Arboretum 59(2): 156-169. https://doi.org/10.5962/p.324728 Tomlinson PB (1986) The Botany of Mangroves. 1* edn. Cambridge University Press, Cambridge, 413 pp. Tomlinson PB (2016) The Botany of Mangroves. 2"! edn., Cambridge University Press, Cambridge, 418 pp. Turland NJ, Wiersema JH, Barrie FR, Greuter W, Hawksworth DL, Herendeen PS, Knapp S, Kusber WH, Li DZ, Marhold K, May TW, McNeill J, Monro AM, Prado J, Price MJ, Smith GF (2018) International Code of Nomenclature for Algae, Fungi, and Plants (Shen- zhen Code) Adopted by the Nineteenth International Botanical Congress Shenzhen, China, 2017. Koeltz Botanical Books, Regnum Vegetabile 159, Glashitten. https:// doi.org/10.12705/Code.2018 WFO (2025) World Flora Online. http://www.worldfloraonline.org PhytoKeys 259: 1-25 (2025), DOI: 10.3897/phytokeys.259.157847 95