Monographs Details: Ectropothecium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants small to medium-sized, in often lustrous, soft or stiff, green to golden, often extensive, thin mats. Stems creeping, irregularly but freely branched to regularly pinnate, the branches mostly simple; in cross-section without a hyalodermis, with small thick-walled cells surrounding larger thinner-walled cells, central strand present or absent; pseudoparaphyllia filamentous to foliose, the outer ones narrowly foliose; axillary hairs with a single short brown basal cell and 1 to several elongate hyaline distal cells. Stem and branch leaves similar, crowded, typically falcate-secund, the apices often pointing toward the substrate, sometimes erect, lanceolate to ovate-lanceolate, symmetric or somewhat asymmetric, gradually short- to long-acuminate, concave, often plicate, not or scarcely decurrent; margins serrate to serrulate above, entire below, mostly plane or erect; costa short and double, sometimes to 1/4 the leaf length, or absent; cells linear to linear-flexuose, mostly smooth, rarely prorulose, thin- to firm-walled, becoming shorter, broader, thicker-walled and porose toward the insertion; alar cells few in extreme basal angles, quadrate to short-rectangular, not thick-walled, typically with a single hyaline, ± inflated cell in each basal angle. Asexual propagula none. Autoicous or dioicous. Perichaetia often conspicuous; leaves oblong-lanceolate, long-acuminate, sometimes plicate; margins serrate to serrulate above, entire below, plane; costa usually none; cells linear, smooth, thick-walled, porose, becoming shorter and broader toward the insertion; alar cells not differentiated. Setae elongate, smooth, reddish, twisted, curved just below the urn; capsules horizontal to pendent, small, ovoid, constricted below the mouth when dry; exothecial cells quadrate to rectangular, mostly collenchymatous; annulus differentiated; operculum short conic-rostrate; peristome double, exostome teeth shouldered, bordered, on the front surface cross-striolate below, coarsely papillose above, trabeculate at back; endostome with a high basal membrane, segments broad, keeled, narrowly perforate, ca. as long as the teeth, cilia in groups of 1-3. Spores spherical, finely papillose. Calyptrae cucullate, naked or sparsely hairy, smooth.
Discussion:Discussion. Ectropothecium is characterized by often regularly pinnate plants with falcate-secund leaves and scant alar development. The predominant feature of the genus, and the only one that really separates it from Hypnum, is the short, ovoid capsule. Collenchymatous exothecial cells additionally argue for generic distinctness. The narrowly foliose outer pseudoparaphyllia are very helpful in identification, though admittedly are a tedious character to demonstrate.
The genus is the “Hypnum” of the tropics and many first-time visitors to equatorial latitudes are easily deceived. However, the falcate-secund leaves often pointing to the substrate and the small capsules are helpful characters. The genus is particularly well developed (and troublesome) in the Old World tropics.
When Mitten (1868) described Ectropothecium, he included five species in the genus. An examination of the five species reveals considerable differences between them and not all are equally best chosen for a lectotype. Ectropothecium pacificum Mitt., the only species described as new when the genus was proposed, has leaves that are not falcate-secund and have prorulose laminal cells. Ectropothecium tutuilum (Sull.) Mitt, is similarly anomalous in the genus. Both of these species should perhaps be transferred into Ctenidium or a related genus. Ectropothecium fuscescens (Hook. & Am.) Mitt, is currently accommodated in Vesicularia. Of the two remaining, E. buitenzorgii (Bél.) Mitt, and E. sodale (Sull.) Mitt., both are well within the limits of Ectropothecium as it is commonly interpreted. However, Mitten only incidentally transferred Hypnum buitenzorgii Bél. into the genus and for that reason I designate E. sodale as the lectotype for Ectropothecium. It is quite similar even to our common West Indian species but the plants differ significantly in their much smaller stature.
Ectropothecium is represented in the West Indies by a widespread, common species and a very restricted, rare species.