Monographs Details: Hypnella
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants slender to medium-sized, in ± dull or lustrous, whitish green to golden or reddish, mostly flat, dense or thin mats. Stems creeping, red, irregularly but freely branched, the branches not differentiated, not or obscurely complanate-foliate; in cross-section without a hyalodermis, with a few rows of small colored thick-walled cells surrounding large thin-walled cells, central strand none; rhizoids confined to oldest portions of stems, tufted, slightly roughened when mature; pseudoparaphyllia large, foliose; axillary hairs 2-celled, with a short brown basal cell and an elongate hyaline distal cell. Leaves closely placed, not contorted when dry, mostly erect-spreading, sometimes falcate-secund, lanceolate to oblong-lanceolate to ± oblong, obtuse or acute to piliferous, concave; margins not bordered except sometimes the marginal row smooth, serrate to serrulate throughout, mostly plane, sometimes erect or broadly incurved; costa double, usually ending ca. 1/3-3/4 the leaf length, not projecting or only slightly so at extreme apex; cells long-hexagonal to linear, pluripapillose, the papillae seriately arranged over the lumina, simple or branched, thin- to thick-walled, ± porose, apical cells mostly not differentiated, becoming shorter, thicker-walled and smooth toward the insertion; alar cells not differentiated. Asexual propagula none. Autoicous, synoicous, or dioicous. Perichaetia small, inconspicuous, along stems; leaves pale, ± erect to erect-spreading, similar to vegetative leaves but usually with a weaker costa and cells papillose only in upper 1/3 of leaf. Setae elongate, roughened at apex, reddish, curved at apex; capsules inclined to horizontal to ± pendent, conic-cylindric, ± symmetric; exothecial cells quadrate to short-rectangular, firm-walled, collenchymatous; annulus not differentiated; operculum short-rostrate from a conic base, or with a long, pale, fragile rostrum, the basal cells of operculum sometimes differentiated; columella broadly cylindric, short, ending below midurn; peristome double, attached at the mouth, exostome teeth narrowly triangular, scarcely bordered, not shouldered, on the front surface reddish, with a broad median furrow with a zig-zag line down it, or not furrowed with a zig-zag median line, the plates cross-striolate below, coarsely papillose above (just above apical end of furrow), moderately trabeculate at back, yellow; endostome yellowish, smooth to finely papillose, with a fairly high basal membrane, segments keeled, not or narrowly perforate, with baffle-like crosswalls, ca. as long as the teeth, cilia none. Spores spherical, finely papillose. Calyptrae mitrate, covering operculum and upper urn, irregularly lobed at base, ± plicate, naked, smooth or roughened.
Discussion:Hypnella (Müll. Hal.) A. Jaeger, Ber. Thãtigk. St. Gallischen Naturwiss. Ges. 1875-76: 365. 1877; Hookeria sect. Hypnella Müll. Hal., Syn. Musc. Frond. 2: 208. 1851; Hookeria subgen. Hypnella (Miill. Hal.) Hampe, Verh. Zool.-Bot. Ges. Wien 21: 391. 1871.
Hookeria sect. Hypnella subsect. Euhypnella Miill. Hal., Syn. Muse. Frond. 2: 211. 1851.
Neohxpnella E. B. Bartram, Contr. U.S. Natl. Herb. 26: 104. 1928.
Discussion. Hypnella is distinguished from all other Hookeriales in the seriate papillae over the lumina of the leaf cells. It is characterized by linear leaf cells and essentially unbordered leaves. Sometimes the marginal row of laminal cells are not papillose, but they are otherwise undifferentiated. The costa is usually strong,m regularly ending below midleaf in only one species. The capsules are distinctively conic-cylindric (when dry) and the upper portionof the seta is coarsely papilliose to tuberculate. The genus is probably most closely related to the Callicostella complex, but differs in the longer, pluripapilose leaf cells.
Hypnella was recently reviewed by Crosby et al. (1985) and Allen (1986), who provided keys, synonymy, illustrations, and discussion but not descriptions. Like Crosby et al., I have included Neohypnella in Hypnella. It differs from Hypnella solely in the absence of an exostomial furrow. Another alternative would be to recognize two genera on the basis of leaf shape, with H. pilifera (Hook. & Wils.) A. Jaeger and H. leptorrhyncha as true Hypnella, and H. pallescens and H. diversifolia as Neohypnella. However, at present I prefer a single genus.
Crosby et al. transferred Hypnella to the Sematophyllaceae (Hypnales) because of a supposed relationship to Taxithelium and Glossadelphus ( = Phyllodon of Hypnaceae in this work). Indeed there are similarities, but the differences, which they ignored, seem overwhelmingly to support a Hookeria-lean alliance. Among these are the strong double costa, lack of alar differentiation, 2-celled axillary hairs, mitrate calyptrae, and baffle-like crosswalls on the endostomial segments. Therefore, I leave Hypnella in the Hookeriales without reservation.