59. ASCHISMA Plate 81.

Aschisma Lindb., Utkast Nat. Grupp. Eur. Bladm. 28, 1878. Type: Aschisma carniolicum (Web. & Mohr) Lindb.

Phascum subg. Aschisma (Lindb.) Kindb., Eur. N. Amer. Bryin. 2: 403, 1897.

Plants very small, gregarious or forming a thin green turf. Stems seldom branching, ca. 0.2 µm in length, transverse section rounded-pentagonal, central strand present, weak, sclerodermis not well differentiated, hyalodermis absent; axillary hairs ca. 3 cells in length, basal cell thicker walled. Leaves incurved and tubulose when dry, weakly spreading when moist, oblong or triangular to short-lanceolate, often falcate and plicate on one side, 0.6–1.0 µm in length, upper lamina broadly channeled, margins plane to occasionally weakly incurved, entire to sharply serrulate above midleaf, sometimes bordered above, below or throughout by 1–3 rows of weakly papillose, elongate cells; apex broadly or rounded-acute; base little differentiated in shape; costa excurrent as a sharp mucro, this occasionally rough or denticulate, superficial cells elongate both ventrally and dorsally, 2–4 rows of cellsacross costa ventrally at midleaf, costal transverse section circular to elliptical, two stereid bands present, mostly substereid ventrally, often also substereid dorsally, epidermis not differentiated, guide cells 2–4 in 1 layer, hydroid strand apparently absent or occasionally present; upper laminal cells quadrate to occasionally short-rectangular, 9–12 µm in width, 1:1(–2), walls evenly thickened, superficially flat or bulging only ventrally or on both exposed surfaces; papillae stout, bifid, crowded, scattered or centered over lumens, ca. 4 per lumen; basal cells strongly differentiated, rising higher along margins in a weak vee, rectangular, little wider than upper cells, 3–5:1, walls very thin to evenly thickened. Monoicous. Perichaetia terminal, inner leaves long-elliptical, to 1.5 µm in length, concave or not sheathing, lower cells oblong. Antheridia paroicous in axils of bracts or in stalked autoicous buds at base of the perichaetiate plant. Seta very short, ca. 50 µm in length, 1 per perichaetium, hyaline, straight; capsule cleistocarpous, 0.3 µm in diameter, yellowish brown, spherical, with a small blunt apiculus (ca. 30 µm in length), exothecial cells rectangular, mostly ca. 13–18 µm in width, 4–5:1, circling capsule longitudinally in several even bands with the appearance of a palisade, stomates absent, annulus absent; peristome teeth absent. Calyptra conic, split once or twice, rough, 0.2–0.3 µm in length. Spores large, 18–24 µm in diameter, yellowish brown, essentially smooth to spiculose-papillose. Laminal KOH color reaction yellow.

A genus widely distributed in the Mediterranean area and disjunctive to central North America; growing in dry climates on soil, occasionally under translucent rocks in exposed situations.

The most prominent traits of this distinctive genus are the dry habitat; small size of the plants; spherical, cleistocarpous capsules with yellow, rectangular cells arranged in neat encircling bands, lacking stomates (Pl. 81, f. 9–10); the weak, hyaline seta; the falcate leaves usually with a distinct border of epapillose cells (Pl. 81, f. 5, 6, 16) and the leaf base not differentiated in shape; and the costa with usually merely substereid cells in two bands (Pl. 81, f. 7, 8, 17). As is the case with Tetrapterum and Tortula sect. Schizophascum, both Pottioideae but rather distantly related, the capsule tends to rupture along the transverse walls at the butt ends of the exothecial cells, which are superficially rather thick-walled.

Aschisma carniolicum and A. kansanum are fairly distinct in the material seen. The latter (Pl. 81, f. 12–17) has more strongly bordered and serrulate margins, more strongly bulging upper laminal cells with centered (not scattered) papillae, a larger, more strongly denticulate mucro, and spores less ornamented and toward the small end of the size range for the genus. The protonema of A. kansanum survives arid conditions under translucent pebbles, ultimately producing leafy axes and sporophytes peripherally (Cridland 1959); this scenario is also the case with Bruchia brevifolia (Bruchiaceae) (cf. Rushing 1989) and, at least occasionally, Syntrichia inermis (Weger & During 1989).

Additional literature: Andrews (1915), Crdenas (1988), Sérgio (1972a).

Number of accepted species: 2.

Species examined: A. carniolicum (BUF, NY), A. kansanum (NY).