27. Stegonia Venturi, Rev. Bryol. 10: 96. 1883.
[Greek stego, cover, alluding to concave, protecting leaves]
Richard H. Zander
Pottia sect. Stegonia (Venturi) Müller Hal.
Plants gregarious, bulbiform, white to whitish green distally, brown proximally. Stems to 3 mm; hyalodermis absent, sclerodermis absent, central strand present; axillary hairs ca. 3-6 cells in length, proximal 2 cells firm-walled. Leaves appressed when dry, appressed or loosely involute distally, weakly spreading when moist; nearly circular to very broadly ovate, sometimes elliptic, adaxial surface deeply concave, ca. 1.5-2 mm; base not differentiated, proximal margins not differentiated; distal margins broadly recurved to revolute, occasionally plane or weakly incurved, commonly serrulate near apex, occasionally entire, distal 1/4-1/3 of leaf usually hyaline, of rhomboid thick-walled cells; apex broadly acute or occasionally rounded; costa thin, excurrent as a flexuose hyaline awn or occasionally percurrent or subpercurrent, adaxial epidermal cells forming a bulging adaxial ridge, adaxial cells short-rectangular, bulliform (bulging, thin-walled), in ca. 3-4 rows, adaxial outgrowths rare, lamelliform, rounded or serrate and papillose; transverse section round, adaxial epidermis present, of bulliform cells, adaxial stereid band absent, guide cells 2 (often absent distally) in 1 layer, hydroid strand present, large (occasionally absent distally), abaxial stereid band present (occasionally substereid), round in section, abaxial epidermis absent distally, present proximally; proximal cells differentiated across leaf, rectangular, occasionally bulging, little differentiated or to 30 µm wide, to 4:1, walls of proximal cells often somewhat thicker than distal cells; distal medial cells rhomboid or hexagonal, grading to elongate rhomboid or hexagonal distally, often hyaline distally, 13-22 µm wide, 2-3:1, 1-stratose; papillae absent, cell walls usually thin medially and thick-walled near apex, especially on the abaxial superficial walls, convex on both sides. Specialized asexual reproduction absent. Sexual condition monoicous (paroicous or autoicous); perichaetia terminal, interior leaves little differentiated. Seta 0.2-1.2 cm or very short (70-100 µm). Capsule stegocarpous or cleistocarpous, theca exerted, ovate-cylindric and often slightly curved, to 1-2 mm; or immersed, ovate and very shortly apiculate, ca. 0.7 mm, annulus absent or of 2-3 rows of persistent, vesiculose cells; operculum absent or short-rostrate; peristome teeth absent, rudimentary or 16, cleft to near base, occasionally perforate, ligulate, straight, to 125 µm. Calyptra cucullate. Spores 20-45 µm. KOH distal laminal color reaction yellow.
Species 3 (2 in the flora): w North America, Mexico, Europe, Asia, Africa, Antarctic.
The capsules of Stegonia exhibit a reduction series (R. H. Zander 1993): one species is peristomate, another cleistocarpous, while the third, of northern Africa, is stegocarpous but eperistomate. Both species in the flora area have perichaetial leaves with a leaf apex of hyaline, elongate, rectangular cells (this variable in S. latifolia) similar to that of the arctic Hilpertia velenovskyi, but smaller, proximal leaves similar to those of Tortula acaulon.