36. GYMNOSTOMIELLA Plate 48.

Gymnostomiella Fleisch., Musci Fl. Buitenzorg 1: 309, 1904. Type: Gymnostomiella vernicosa (Hook.) Fleisch.

Gymnomitriella Sak., Bot. Mag. Tokyo 56: 221, 1942, err. pro. Gymnostomiella Fleisch.

Pottia sect. Splachnobryella C. Müll., Gen. Musc. Fr. 389, 1900. Type: Pottia vernicosa (Hook.) Hampe.

Delicate plants in dense tufts or mats, light green to blackish green above, brown below. Stems short, often branching, 1.5–6.0 mm in length, transverse section rounded-pentagonal, central strand present, comparatively large, sclerodermis absent or weak, hyalodermis absent; axillary hairs ca. 3 cells in length, moniliform, basal cell with thicker walls than the distal cells; rhizoids present below. Leaves erect or laxly spreading when dry, erect to spreading, lax when moist, obovate to oblong-obovate, larger above, 0.3–0.4 mm in length, upper lamina flat, margins plane, crenulate above by bulging cell walls, occasionally serrulate, occasionally with 1 or 2 additional large teeth above; apex rounded or very broadly acute, occasionally apiculate by a sharp, conical cell; base not differentiated in shape; costa slender and ending at midleaf or ending near apex, seldom percurrent, superficial cells on both sides elongate, ca. 2 rows of cells across costa ventrally at midleaf, costal transverse section elliptical, stereid band single, small, present centrally, often absent and costal section appearing homogeneous, epidermis absent ventrally and present dorsally, guide cells 2 in 1 layer, hydroid strand absent; upper laminal cells quadrate to hexagonal, occasionally longer than broad, 12–18 µm in width, 1(–2):1, walls thin, delicate, superficially convex on both sides; 1–3 small, simple, hollow, conical papillae per lumen, scattered over lamina; basal cells weakly differentiated across lamina, rectangular, little wider than upper cells, 2–3:1, walls thin. Propagula elliptical to clavate, to 280 µm in length, with ca. 6 transverse and 6 inner longitudinal walls, consisting of about 14 cells, borne in leaf axils or on ventral surface of leaves, sometimes 1–3 in a cup-like terminal rosette of leaves. Dioicous. Perichaetia terminal, inner leaves ovate, to 0.7 mm in length, sheathing, smooth, lower cells laxly rectangular, paraphyses moniliform. Perigonia terminal, paraphyses absent, plants often small, nearly stemless. Seta 3–6 mm in length, 1 per perichaetium, yellowish brown, twisted clockwise; theca 0.6–0.8 mm in length, black or brown, often shiny as if varnished, ovate to short-elliptical, exothecial cells large, rounded-hexagonal, 35–55 µm in diameter, mostly thin-walled, stomates phaneropore, at base of theca but often absent, annulus of about 2 rows of little-differentiated cells; peristome teeth absent. Operculum relatively large, obliquely rostrate from a low-conic base, 0.8–1.0 mm in length, cells weakly twisted clockwise. Calyptra cucullate, smooth, ca. 1.3 mm in length. Spores 11–15 µm in diameter, light brown, finely papillose. Laminal KOH color reaction yellow, or negative to black, or pink to deep purple. Reported chromosome number n = 13.

This is a small genus of southern and eastern Asia, Australia, northern and central Africa, subtropical and tropical North America, Central America, the West Indies and Brazil; found on limy rock usually in association with cyanobacteria (as is the case with Luisierella barbula).

In the absence of a peristome, this genus is placed in the Pottiaceae largely because of its papillose, obovate or spathulate leaves (Pl. 48, f. 3, 5, 8). Although without obvious close relatives, it has some similarity to the genus Chenia and Hennediella (Pottioideae) through the large hyaline laminal cells, simple papillae, and serrulate upper margins. Cladistic analysis indicates that a better phylogenetic hypothesis would be placement in the Barbuleae. Unusual characters are the central location of the single (sub)stereid band (Pl. 48, f. 9–11), the moniliform axillary hairs (approached in shape by the weakly bulging cells of the hairs of Molendoa species), the often nearly spherical capsule with unusually large exothecial cells and stomates often absent, and odd variation in KOH color reaction of the lamina, including black and purple. The possible relationships of Gymnostomiella with the Splachnobryaceae are discussed by Andrews (1949) and Crum (1949) and in an overview of the Splachnobryaceae by A. Koponen (1981). A convenient key to the species of Gymnostomiella was constructed from descriptions by Sloover (1977).

The propagula of G. vernicosa (Pl. 48, f. 4) are borne in leaf axils and in clusters of 1–3 in a somewhat swollen cup-like terminal rosette of ovate leaves with the general appearance of a perigonium. The propagula, with their clavate shape, internal transverse and longitudinal cross walls, are somewhat similar to antheridia. Thus, the propaguliferous sterile plants may easily be mistaken for perigoniate plants. Also, Fleischer (1902–22, Vol. 1, p. 310) correctly indicated that the perigonia of actual perigoniate plants of G. vernicosa, which differ from the propaguliferous sterile plants by being nearly stemless, lack the paraphyses usually expected in perigonia.

Of some significance is the relatively tiny size of the leaves in respect to that of the stem, sporophyte and propagula, in conjunction with the leaves' simple anatomy and serrulate upper margins. The leaves are apparently heterochronically paedomorphic (cf. discussion of Mishler 1986a of this phenonemon in Tortula) in that they may not have developed much beyond the “scale leaf” stage of very young shoots. It would be interesting to attempt to “force” the mature stage by modifying developmental processes (cf. Basile & Basile 1984).

Redfearn (1991) recently synonymized the American G. orcuttii (Pl. 48, f. 12–16) with the Asian G. vernicosa. These two taxa are here conservatively retained as separate species as the former often has multipapillose upper laminal cells and the latter unipapillose cells. Gymnostomiella orcuttii is, however, much like the Asian G. burmensis, and the variation thus may not be geographical. In any case, a revision of all species of the genus is sorely needed, and considerable synonymy might be expected, in all probability supporting Redfearn's evaluation.

Additional literature: Eckel (1985b), Potier de la Varde (1953), Schornherst (1944), Seki and Miyagi (1980), Stone (1985), Vital (1984).

Number of accepted species: 6.

Species examined: B. burmensis (FH), G. longinervis (NY), G. monodii (PC), G. orcuttii, G. vernicosa (BM).