56 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, 28 Sept. 2018, No. 2 
protrude (e.g., Fig. 5H, J). Other studies of Louteridium pollen have noted the following ranges of 
diameters: 125 to 230 pm (nine species; Richardson 1972), 140 pm ( L. donnell-smithii; Raj 1961), 
187 to 206 pm ( L. parayi; Palacios Chavez 1975), and 120 to 130 pm ( L. donnell-smithii ; Scotland 
1993). 
Pollen of Louteridium differs from all other genera of Acanthaceae (including Trichantheri- 
nae). Pollen of core Trichantherinae has been described as “loxodicolporate” (Daniel 1988, 1998, 
2015) and as “rotationally symmetric” by Vasanthy and Pocock (1986); all five genera in this 
latter clade have pollen globose-oblong to globose-elongate, 2-colporate, polypseudocolpate, and 
with sculptural features of one face oriented 90° out of phase with those of the opposite face (e.g., 
Daniel 1998, fig. 3; Tripp et al. 2013, fig. 14; Daniel 2015, fig. 1). This type of pollen appears to 
be unique among extant pollen-bearing plants (although also known in the fossil record; see 
discussions in Tripp and McDade 2014 and Daniel 2015). Among other Ruellieae, pollen of 
Louteridium is similar to that of Brunoniella Bremek. and Acanthopale C.B. Clarke (e.g., Tripp et 
al. 2013, fig. 14); all three genera are pantoforate with ± similar interapertural ornamentation. 
Pollen of Louteridium appears to be unique among Acanthaceae by the combination of these sculp¬ 
tural elements combined with the exceptionally large size of the grains and high number of aper¬ 
tures. Pollen of Brunoniella and Acanthopale (Raj 1961; Scotland 1993; Tripp et al. 2013; and 
additional sampling of limited materials available) varies in size from 40 to ca. 97 pm in diameter 
(or longest axis), and appears to have fewer than 50 apertures. Palacios Chavez (1975) noted the 
exceptionally large size of pollen among numerous bat-pollinated or presumably bat-pollinated 
flowers, including L. parayi. Pollen of that species is typical for the genus as a whole, and bat 
visitation/pollination for species of Louteridium is discussed below. 
Seeds. — The relatively large (up to 8 mm long and 6.4 mm wide) seeds are disposed in two 
rows in each locule of the capsule. Little variation among species was observed for most seed char¬ 
acteristics (Fig. 7). Seeds are discoid (0.40 to 1.23 mm thick) and vary in outline from subcircular 
to subcordate to subellipsoid. The two flat surfaces vary from smooth to wrinkled and sometimes 
bear papillae or tubercles, but lack trichomes. Both shape and surface ornamentation sometimes 
varies within a species. The marginal region is somewhat swollen and the peripheral edge is 
furrowed and densely pubescent with appressed hygroscopic trichomes. When dry, these trichomes 
are sometimes inconspicuous and appear as a solid to irregularly eroded peripheral band, but when 
moistened the trichomes expand to ca. 0.5 mm long (Fig. 7C, K). Most species bear up to 16 seeds 
per capsule; however, L. parayi has up to 18, L. tamaulipense has up to 20, and L. brevicalyx and 
L. rzedowskianum have up to 24. 
Chromosome Numbers 
No chromosome numbers have been published for Louteridium. Among other Trichantherinae, 
several high numbers (the highest reported for Acanthaceae) have been published for Sanchezia 
oblonga Ruiz & Pav. ( n = ca. 66, Grant 1955; n = 68, Singh 1951 and Kaur 1970; all reported as 
S. nobilis Hook.f.) and S. parvibracteata (n = 40, Narayanan 1951; n = ca. 36 to 40, Daniel 2018). 
Chromosome counts were attempted for several years by Daniel and the late T.I. Chuang for other 
genera of Trichantherinae, including Bravaisia and Louteridiu, using techniques noted by Daniel 
et al. (1984) and Daniel (2018). Conclusive counts from meiotic samples of these genera proved 
elusive; for the most part, only approximate counts were obtained (Table 2), and even the non- 
approximate counts noted herein may not represent definitive chromosome numbers for these 
species. Problems encountered in our cytological studies included: few pollen mother cells (which 
are very large; cf. Daniel 2018) in each anther; chromosomes irregularly shaped, consisting of 
distinctly different sizes, and either clumped or otherwise not clearly delimited; apparently 
