42 
PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES 
Series 4, Volume 65, 28 Sept. 2018, No. 2 
genus, known from a single species at the time, among the taxa with contorted corolla aestivation 
in its own tribe, Louteridieae, and noted its large, distinctive pollen and three calyx lobes. 
Bremekamp (1965:27) maintained tribe Louteridieae as distinct from Ruellieae on the basis of the 
“rather aberrant structure” of its pollen, and placed it in subfamily Ruellioideae. Recent classifica¬ 
tion schemes have treated the genus as Acanthoideae: Ruellieae: Ruelliinae (e.g., Scotland and 
Vollesen 2000), and most recently as Acanthoideae: Ruellieae: Trichantherinae (Tripp et al. 2013). 
In a comprehensive taxonomic revision of Louteridium, Richardson (1972) recognized nine 
species: L. brevicalyx, L. chartaceum, L. conzattii, L. costaricense, L. donnell-smithii, L. koelzii, 
L. mexicanum, L. parayi, and L. tamaulipense. Since then, Louteridium rzedowskianum (Rze- 
dowski 1973; Daniel 1984, 2017) and L. dendropilosum (Daniel 2017) have been described. Also, 
in an account of the genus in Chiapas, Daniel (1995) treated L. conzattii as conspecific withT. mex¬ 
icanum and recognized L. purpusii as the correct name for the species treated as L. mexicanum by 
Richardson (1972). Richardson (1972) noted that species of Louteridium were poorly known and 
infrequently collected. Indeed, he was able to study only 71 collections (56 were cited) of the 
genus, six species were known to him by only one or two collections, and he made observations on 
a single species in nature. 
In the present contribution, which builds on Richardson’s (1972) important revision, 315 
collections were studied, observations were made on six species in nature, and four species were 
studied in cultivation. As a result of our work, 11 species are herein recognized comprising a mono- 
phyletic Louteridium, which is sister to the other five genera of Trichantherinae (i.e., “core Trichan¬ 
therinae”). Only one species is now known from fewer than four collections. Of the two sections 
of the genus recognized by Richardson (1972), one (section Tetrandrium ) is maintained based on 
morphological, molecular, and habitat distinctions. Section Louteridium is revealed to correspond 
to two sections that are morphologically and ecologically similar, but which comprise separate 
clades within the genus. 
Materials and Methods 
Specimens and Living Plants. — More than 750 herbarium specimens representing 315 
collections of all species of Louteridium were examined from 42 herbaria. In rare cases, when a 
digital image of a specimen was studied (via http://plants.jstor.org/ or on the website of the herbar¬ 
ium cited), “image seen” is indicated. Four species were cultivated in pots at a greenhouse or on a 
lighted plant stand by a window in San Francisco from cuttings or seeds collected in nature. Plants 
of the following species (source locality and voucher number, which consists of the field collection 
number + cv) were subjected to various treatments and observations: L. brevicalyx (Mexico: 
Michoacan; Daniel & Steinmann 11913cv), L. chartaceum (Belize: Belize; Daniel & Butterwick 
5905cv), L. dendropilosum (Mexico: Oaxaca; Daniel et al. 11894cv), and L. mexicanum (Mexico: 
Chiapas; Breedlove & Daniel 70879cv). Field observations on these, and two other species (i.e., 
L. donnell-smithii, L. parayi), were also conducted in native plant habitats. The observations, treat¬ 
ments, results, and interpretations are discussed under the appropriate sections below. 
ddRAD Library Preparations. — To reconstruct phylogenetic relationships within 
Louteridium, facilitate understanding the evolution of morphological features among species, and 
test monophyly of Richardson’s (1972) sections Louteridium and Tetrandrium, we generated and 
used ddRADseq data spanning multiple accessions of most species as follows. DNA was extract¬ 
ed from 30 samples of Louteridium representing all 11 species (Table 1). Of these, a minimum of 
two different collections were sampled for nine species; only one accession each of L. brevicalyx 
and L. koelzii were sequenced. Additionally, we extracted DNA from four species outside of 
Louteridium (one Petalidium plus three Ruellia; Table 1) but within tribe Ruellieae (Tripp et al. 
