DANIEL: NEW AND RECONSIDERED MEXICAN ACANTHACEAE XII 
141 
4, 60-80 mm long, filaments glabrous distally, pubescent with eglandular trichomes near base (i.e., 
fused portion of pairs), pairs fused at base up to 9 mm, thecae 8-10.5 mm long; staminode con¬ 
sisting of a rodlike projection 0.6 mm long in dorsalmost position; pollen subspheroidal to spheri¬ 
cal (P:E = 0.96-1.04), pantoporate, 114-131 pm in diameter, exine surface microrugulate to 
microverrucate and with overstory of gemmae and/or bacculae. Style 70-101 mm long, distally 
glabrous, pubescent with eglandular and glandular trichomes near base, stigma equally 2-lobed, 
lobes flattened, broadly elliptic, 1-2 mm long, 1-1.4 mm wide. Capsule 25-28 mm long, densely 
pubescent with erect glandular trichomes 0.05-0.5 mm long and with an overstory (sometimes 
sparse) of erect to flexuose (sometimes dendritic) eglandular trichomes to 1.4 mm long, stipe 
2.5-3.5 mm long. Seeds to 16 per capsule, 5.2-7 mm long, 5-6.4 mm wide, surfaces smooth and 
lacking trichomes, margin ± thickened, densely pubescent with hygroscopic trichomes expanding 
to 0.5 mm long when moistened (appearing as a ± solid to irregularly eroded peripheral band when 
dry). 
Phenology.— Flowering: February-March; fruiting: March-April. As in some other species 
of Louteridium, flowering takes place during the dry season when leaves are often absent (e.g., 
February). Near the end of the dry season (e.g., late March) when flowering is waning and fruits 
are mature, a new flush of vegetative growth appears from axils of clustered leaf scars at the base 
of the inflorescence (which eventually falls away). As the cluster of new leaves develops (fig. 7), 
intemodal stem growth takes place between at least one of the pairs and the remaining cluster (e.g., 
the young stems of the description above). 
Distribution and habi¬ 
tat.— Southern Mexico (central 
southern and southeastern Oaxa¬ 
ca; Fig. 6); plants occur on 
karstic slopes of streams in ever¬ 
green seasonal forest (selva 
mediana subperennifolia) and 
tropical deciduous forest (bosque 
tropical caducifolio) with Beau- 
carnea, Brosimum, Bursera, 
Lonchocarpus ) at elevations 
from 600 to 750 m. 
Illustrations. — Figures 7, 8. 
Conservation. — This species is known only from the Sierra Madre del Sur and the Isthmus 
of Tehuantepec in Oaxaca, consisting of two locations ca. 137 km apart. The EOO is 32.1 sq. km. 
None of known occurrences is on protected lands. At the type locality in 2014, about 50 mature 
plants were observed in an area of ca. 2250 square meters on rocky limestone slopes above a 
stream. Much or all of this locality has since been destroyed by road-building activities at that site 
(S. Salas, pers. comm, in March 2015). With on-going development of these and other types (e.g., 
agricultural) of human disturbances at one of the two locations, a decline in populations or popu¬ 
lation sizes has been observed and would seem likely to continue. Thus, a preliminary assessment 
of Endangered (En) is proposed for this species (Bl, a, b; IUCN 2017). 
Paratypes. — MEXICO. Oaxaca: Distr. Pochutla, Mpio. San Miguel del Puerto, Arroyo 
Arena, ca. 100 m downstream from jet. Rio Laja, ca. 3 km SE of Rancho Dioon toward Xadani, 
T. Daniel, E. Lott, J. Pascual, andN. Salas M. 11894 (CAS, MEXU); Mpio. El Barrio, 9 kmN [sic] 
de El Barrio, Cerro Palmasola, antena microondas [ca. 16°44’32.52”N, 095°05’36.04”W], R. Fer¬ 
nandez N. 4189 (IEB, NY); Distr. Pochutla, Mpio. San Miguel del Puerto, Arroyo Arena, 
102° 100° 
- -i-T" 
98° : 
\ 
- 1 - 
94° 
18°- 
* f 
* Louteridium dendropilosum 
• Louteridium rzedowskianum 
& 
/ , V c 
100 km 
Figure 6. Map of southern Mexico with distributions of Louteridium 
dendropilosum (Oaxaca) and L. rzedowskianum (Guerrero). 
