DANIEL & TRIPP: LOUTERIDIUM : TAXONOMY, BIOLOGY, AND CONSERVATION 53 
merits generally curve upward then downward, forming an arc that is terminated by dangling 
anthers, free of obstructions. Filaments are inserted (i.e., emerge from) the internal surface of the 
corolla tube at or near (i.e., a few millimeters distal to) the junction of the narrow proximal portion 
and the throat. Anthers of all stamens in Louteridium bear two elongate (6.5 to 17 mm) thecae that 
are introrse, resulting in a nototribic flower. 
In sections Louteridium and Parcostamium, there is a flat and somewhat quadrangular flange 
(ca. 4 to 5 mm long and wide) of tissue that is developed to a greater (e.g., L. mexicanum ) or 
lesser (e.g., L. donnell-smithii ) extent on both sides of the basal portion of each filament. On the 
posterior side of each filament the flange bears a short (0.5 to 3 mm long) triangular to subulate 
staminode; thus, the two staminodes are nearest to each other and between the filaments on the 
posterior side of the corolla tube. The adjacent flanges bearing staminodes from each filament do 
not fuse with one another. One or more staminode-like appendages are sometimes present on the 
distal portion of the flange on the opposite (anterior) side of the filament, but no veins go to this 
region. Flanges of both filaments (usually on the anterior side of each filament) taper as they extend 
4 to 6 mm toward the base of the narrow proximal portion of the corolla tube. Collectively the 
flanges from the base of the filaments form a barrier or a portion of the “filament curtain” sensu 
Manktelow (2000) that creates a nectar chamber in which the ovary, proximal portion of the style, 
and nectar disk occur. Because the curtain may be oriented obliquely, the chamber does not always 
occupy the entire narrow proximal portion of the corolla tube. In L. parayi of section Parcostami¬ 
um, the narrow proximal portion of the corolla tube is greatly reduced in length. In this species, 
there is a very pubescent flange along the base of the equally pubescent basal portion of each fila¬ 
ment. Based on the position of staminodes in sections Louteridium and Parcostamium, the fertile 
pair of stamens in this section corresponds to the anterior pair of androecial elements. 
In section Tetrandrium the four filaments are arranged pairwise in two different configura¬ 
tions. The anterior pair of filaments is inserted a few millimeters proximal to the posterior pair. 
Thus, although the stamens are usually equal in length, during anthesis the anthers of the latter pair 
are presented several millimeters beyond (i.e., in front of) those of the former pair. Each of the ante¬ 
rior filaments is connate with the adjacent posterior filament, such that each connate pair consist of 
two stamens inserted at different heights in the corolla tube. These pairs are connate at their bases 
for varying distances (e.g., 2 to 4 mm in L. chartaceum and 10 mm in L. brevicalyx ) by a pubes¬ 
cent (or somet im es glabrous in L. dendropilosum) flange of tissue from the filaments. Together the 
filament flanges and the lateral invaginations of the anterior portion of the corolla throat noted 
above form a barrier to the nectar chamber similar to that described above for plants with two 
stamens. In L. brevicalyx, the nectar chamber appears to occupy the entire narrow proximal portion 
of the corolla tube. In species of section Tetrandrium, a narrow, pubescent, flange-like extension 
from the non-connate side of each of the proximally inserted filaments tapers 4 to 6 mm down the 
narrow proximal portion of the corolla tube. There is no fusion between the two pairs of connate 
stamens, thus potentially rendering the nectar chamber accessible by probing floral visitors. A 
single staminode, when present or evident, in section Tetrandrium is borne on the inner surface of 
the corolla tube in posterior-most position, between the two connate pairs of stamens in the vicin¬ 
ity of the zone of connation. 
The types of filament curtains occurring among Acanthaceae, and a description of that in 
L. mexicanum, were provided by Manktelow (2000). In what is presumed to be a teretological 
androecium in a dissected flower of L. mexicanum (section Louteridium', Breedlove & Daniel 
78879cv), a third fertile stamen appears to be borne in anterior-most position, and emerges at or 
very near the base of the corolla (ca. 13 mm proximal to the emergence of the remainder of the 
androecium). 
