64 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, 28 Sept. 2018, No. 2 
rescences/flowers produced free from the foliage (inflorescences generally borne above the vege¬ 
tative shoots, which in some species are leafless during the flowering season, and flowers borne on 
elongate pedicels), nocturnal anthesis (currently documented for most species), drab flower color 
(corollas mostly greenish, yellowish, white, or somet im es chestnut to maroon), large flowers 
(corollas 35 to 72 mm long), corolla open bowl- or bell-shaped (bell-shaped with a wide mouth and 
a saccate throat), large anthers (6.5 to 17 mm long), large pollen grains (106 to 143 pm in diame¬ 
ter), and an abundance of hexose-rich nectar (see discussion below). One characteristic often asso¬ 
ciated with chiropterophily is a musky or mouse-like odor, dominated by sulphur-containing 
compounds (e.g., Knudsen and Tollsten 1995). No odor was detected for Louteridium among liv¬ 
ing flowers observed or noted among collectors’ data on herbarium labels. Pollination of Neotrop¬ 
ical Acanthaceae by bats has been documented for Trichanthera gigantea (Acanthoideae: Ruel- 
lieae: Trichantherinae; Steiner 1981; Anonymous 1984; and see discussion in Daniel 2015), 
Harpochilus neesianus (Acanthoideae: Justicieae; Vogel et al. 2004), and Aphelandra acanthus 
Nees (Acanthoideae: Acantheae; Muchhala et al. 2009). Flowers of other Acanthaceae that share 
some or all floral adaptations associated with bat pollination have been noted for some species of 
Ruellia section Chiropterophila (e.g., Palacios Chavez 1975; Ramamoorthy and Lorence 1987; 
Ramamoorthy 1991; Tripp and Manos 2008; Tripp 2010). 
Species of Louteridium that have been noted as likely pollinated by bats include L. chartaceum 
and L. donnell-smithii (e.g., Vogel 1969a; Fleming et al. 2009) and L. parayi (Palacios Chavez 
1975). Based on the preponderance of evidence from floral morphological characteristics, timing 
of anthesis, nectar quantity and sugar composition, and observations on floral visitors, it would 
appear that flowers of all species of the genus are well adapted for, and undoubtedly pollinated by, 
Neotropical bats (Microchiroptera). Louteridium appears to be the largest genus of Acanthaceae 
entirely adapted for pollination by bats. Diurnal visits by hummingbirds have been noted to other 
chiropterophilous flowers of Acanthaceae (e.g., Tripp et al. 2013) and of other families (e.g., Abrol 
2012). It is likely that hummingbirds that visit flowers of Louteridium also play a role in their pol¬ 
lination. 
Floral Rewards/Nectar. — Flowers of two species (L. dendropilosum, L. tamaulipense ) 
were noted to lack any discemable scent (Richardson 1972; TFD, personal observations). 
However, flowers of Louteridium present floral visitors with at least two potential rewards, pollen 
and nectar. The locations on the flowers of both are discussed above (see Morphology). Visitors to 
flowers of Louteridium noted above include small bees or flies, hummingbirds, and bats. Small 
bees and flies were only observed gathering pollen from anthers, and did not make contact with 
other parts of the flower, whereas both hummingbirds and bats were observed either visiting and/or 
interacting with the corolla as well as the reproductive structures. 
Quantities of nectar present in flowers vary among species. Richardson (1972:64) indicated 
that there was “not an abundance” of nectar in flowers of L. tamaulipense that he examined in the 
field. Similarly, no nectar was observed in newly opened or post-mature flowers of either L. den¬ 
dropilosum or L. brevicalyx in their native habitats. However, it is probable that nectar was present 
in corollas of these flowers, but obscured from view by the filament curtain (see Morphology 
above). Indeed, abundant floral nectar (78.6 pi) in a cultivated plant of L. dendropilosum (Daniel 
et al. 11894cv), while not visible because of the invaginations of the corolla and filament curtain 
(Fig. 2L), was located by probing through these obstacles with a micropipette. This situation in 
somewhat similar to corollas of Ruellia conzattii Standi, and R. laslobasensis E. Tripp, which can 
have large quantities of nectar hidden by the filament curtain. By contrast, a plant of L. mexicanum 
{Breedlove & Daniel 70879gh) cultivated in a greenhouse in San Francisco formed pools of nectar 
in the anterior portion of the saccate throat of the corolla tube. In these flowers visible nectar 
