39. HYMENOSTYLIELLA Plate 52.

Hymenostyliella Bartr., Philippine J. Sci. 68: 108, 1939. Type: Hymenostyliella involuta (Card. & Thér.) Bartr.

From Hymenostylium, a genus + i + ‑ella, diminutive; resembling the genus Hymenostylium.

Plants in cushions, yellow-green above, yellow-brown below. Stems branching irregularly, to 3 cm in length, transverse section rounded-pentagonal, central strand strong, sclerodermis present, hyalodermis absent; axillary hairs of 7–10 cells, basal 1–2 yellowish brown; red-tomentose. Leaves involute incurved, curled when dry, spreading-recurved when moist, long-lanceolate, widest just below midleaf, ca. 4.5 mm in length, upper lamina broadly channeled across leaf, margins involute in upper 4/5, plane below, entire or more commonly distantly dentate in upper 1/4; apex narrowly acute; base not differentiated in shape, somewhat decurrent; costa short-excurrent as a mucro, occasionally flexuose or dentate, superficial cells ventrally quadrate to short-rectangular, bulging, once prorulose at distal ends, dorsally elongate, 4–5 rows of cells across costa ventrally at midleaf, costal transverse section semicircular, 2 stereid bands present, epidermis present ventrally, weakly developed dorsally, guide cells 4 in 1 layer, hydroid strand absent; upper laminal cells rounded-hexagonal or somewhat longitudinally elongate, 10–13 µm in width, 1(–2):1, walls thick, trigonous, superficially strongly bulging ventrally, flat dorsally; papillae absent; basal cells weakly differentiated across leaf or somewhat higher along margins, rectangular, similar to upper cells in width, 2–4:1, walls moderately thick-walled, somewhat porose. Dioicous. Perichaetia on short lateral branchlets, inner leaves lanceolate, to 3.0 mm in length, strongly sheathing in lower half, cells long-rhomboidal in lower 4/5. Perigonia lateral, small, gemmate, occurring singly or in clusters. Seta ca. 5–6 mm in length, 1 per perichaetium, reddish brown, twisted clockwise; theca ca. 1.2–1.5 mm in length, reddish brown, obovoid to elliptical, exothecial cells rhomboidal, thick-walled, stomates phaneropore, at base of theca, annulus of 2–3 rows of dark, weakly vesiculose cells; peristome absent. Operculum long-rostrate, longer than the theca, to 1.5 mm in length, cells in straight rows. Calyptra cucullate, smooth, ca. 1.7 mm in length. Spores ca. 10–13 µm in diameter, light brown, essentially smooth. Laminal KOH color reaction yellow. [This description is based on H. llanosii collections at PC and US. Robinson (1971a) recently transferred Timmiella alata Herz. to this genus (without examination of authentic material but probably correctly), saying this species is closely related but is distinguished from H. llanosii by a dorsal costal surface winged with two ridges up to 12 cells in height and a cucullate leaf apex.]

A rare taxon found on rock in wet areas in the Philippines, India and Brazil.

This genus bears an immediate resemblance to Timmiella by the elongate, involute leaf and ventrally bulging-mamillose upper laminal cells (Pl. 52, f. 6), but as Chen (1941) pointed out, the latter genus has a peristome, as well as a bistratose upper lamina. Unusual characters in Hymenostyliella are the strongly involute leaf margins, ventrally bulging-mamillose and trigonous (Pl. 52, f. 4) upper laminal cells, and sporophytes borne laterally on short branches (Pl. 52, f. 1). Saito (1975a) noted the monopodial branching of Hymenostyliella in his discussion of H.japonica (as a synonym of Didymodon japonicus). The long-lanceolate leaf shape and distant teeth of this genus are reminiscent of Tuerckheimia, which differs by the distinctive massive laminal papillae and terminal perichaetium. Robinson (1971a) indicated a similarity to Hyophila (Cladogram 15 bears out a relationship) through the ventrally bulging-mamillose upper laminal cells. Hyophila differs, however, in its spathulate leaves, generally has a hydroid strand, and is acrocarpous; Ganguleea, with laterally borne sporophytes is seemingly more closely related, but see Cladogram 15. The characteristic trigonous areolation is found to greater or lesser degree in genera of other subfamilies, such as Hymenostylium, Leptodontium, Reimersia, Trichostomum and Tuerckheimia.

Number of accepted species: 3.

Species examined: H. llanosii (PC, US).