DANIEL & TRIPP: LOUTERIDIUM : TAXONOMY, BIOLOGY, AND CONSERVATION 51 
that consists of a flower subtended by two homomorphic bracteoles. A bud is commonly present in 
one or both of the axils of the flower (or its pedicel) and each bracteole. From one or both of these 
buds, additional flowers, each subtended by two bracteoles, may develop into a multi-flowered 
dichasium. In Louteridium, the dichasia are sessile or pedunculate in the axil of a bract along a cen¬ 
tral axis, and the one to many flowers are usually borne on elongate pedicels from between the 
bracteoles. Herein, the inflorescences are referred to as racemes when the dichasia are sessile (but 
elongate pedicels are present), racemose thyrses when the dichasial peduncles are very short (e.g., 
1 to 2 mm long), and thyrses when the dichasia are subtended by longer peduncles. Two or more 
of these configurations may occur in the same species, on the same plant, or in the same inflores¬ 
cence (e.g., see below under L. donnell-smithii). As in other Acanthaceae, modifications on this 
pattern are evident among species of Louteridium. For example, the lateral dichasia are often 
expanded via sympodial growth and can appear like lateral inflorescence branches (e.g., L. costari- 
cense, L. tamaulipense ) or short-shoots (e.g., L. chartaceum, L. purpusii ). These are sometimes 
mostly or exclusively basal (proximal) in the inflorescence (e.g., L. tamaulipense). The short- 
shoots are often somewhat tortuous or vary from linear (e.g., L. chartaceum) to fan-shaped (e.g., 
L. purpusii). In L. mexicanum, sympodial expansion of the dichasia can be either contracted or 
expanded and unbranched or branched. 
Flower. — Flowers in Louteridium are nearly always borne on elongate pedicels that vary 
from (6 to) 20 to 105 mm in length. In spite of a gross similarity among flowers of Louteridium, 
there are numerous differences both within and among species. Some floral features are discussed 
in detail below because of either their taxonomic importance or their relevance to the reproductive 
biology of these plants. 
The calyx of Louteridium consists of three lobes, which vary from distinct to basally fused for 
up to 3.5 mm. Because most (or all?) other Acanthaceae have five (rarely four) calyx lobes, the 
three-lobed calyx appears to be a morphological synapomorphy for the genus. Watson (1888:283) 
indicated that the two “upper sepals” were distinct and the lower three were united to the apex. He 
subsequently reversed this interpretation and indicated that the “three upper sepals” were united 
and the “lower two” remained distinct (Watson 1889:85). Bremekamp (1965) indicated that the 
calyx of Louteridium resulted from the fusion of the three anticous lobes. Whether by fusion or 
suppression of lobes, the developmental/evolutionary origin of the three-lobed calyx in Louter¬ 
idium remains unknown. If by fusion, evidence from venation is equivocal. Both the posterior 
(= dorsal) lobe and the two lateral lobes have a single prominent midvein and sometimes one or 
more additional, more or less prominent, veins parallel to it on each side of the midvein (Fig. 4A, 
D, E). The lateral veins (and sometimes the midveins) can be inconspicuous or not evident in fresh 
or dried specimens. Although Watson’s correction in 1889 and Bremekamp’s agreement are possi¬ 
bly correct, none of the lateral veins is clearly identifiable as a “former midvein;” and total 
suppression of two lobes remains a possibility. Indeed, the presence of two additional and much- 
reduced calyx lobes on some flowers of L. brevicalyx (see under that species below) strongly 
suggests suppression. Developmental studies might ultimately determine the origin of the three- 
lobed calyx in Louteridium. 
The three calyx lobes range in size from relatively small (i.e., 5 to 9 mm long in L. rze- 
dowskianum) to subfoliose and larger (e.g., up to 65 mm long in L. costaricense). The lobes vary 
Figure 4 (left). Flowers of Louteridium spp. A, B. L. costaricense (Gonzalez 1977), lateral and frontal views. C. L. don¬ 
nell-smithii (Daniel & Veliz 11337), cream to green-yellow colored form. D. L. donnell-smithii (Daniel et al. 11356), chest¬ 
nut to maroon colored form. E. L. mexicanum (Breedlove & Daniel 70879cv). F. L. purpusii (Velasquez et al. 658). 
G. L. parayi (Daniel & Wendt 5805) showing basally saccate dorsal calyx lobe on two buds at left. H. L. parayi (Breedlove 
24816). Photos by D. Breedlove (H), T. Daniel (C-E, G), J. Gonzalez (A-B), and L. Velasquez (F), used with permission. 
