Megalembidium R.M.Schust.
Megalembidium R.M.Schust., J. Hattori Bot. Lab. 26: 258. 1963.
Kurzia sect. Megalembidium (R.M.Schust.) Grolle, J. Jap. Bot. 39(3): 80. 1964.
Type: Megalembidium insulanum (W.Martin & E.A.Hodgs.) R.M.Schust. (≡Lembidium insulanum W.Martin & E.A.Hodgs.)
Plants dendroid, the main erect shoots and branches isophyllous or nearly so, the plants pale green to pure green, the lower sectors of main axis brownish with age, medium-sized, the leafy axes to 3.5 cm high. Plants with a strongly developed system of basal, creeping, plagiotropic rhizomes, from which arise erect, leafy shoots that distally are copiously and 2–3-pinnately branched; rhizome and leafless sectors of erect axes giving rise to intercalary, geotropic, microphyllous, root-like axes, which in turn give rise to intercalary, considerably more slender secondary branches (“secondary roots”). Branches of erect shoot system crowded distally, regular, determinate in length, on one side of axis of Frullania type, on the opposite side of Microlepidozia type, the ultimate branches often weakly cernuous or circinate, the erect shoots unbranched below. Stems of primary aerial axes rigid, comprised of a hyaloderm of numerous, slightly thick-walled, hyaline or pigmented cortical cells that collapse with age and (1)2–3 subepidermal layers of small, fuscous, strongly thick-walled cells, grading into a medulla of ± thin-walled colorless cells. Leaves unistratose, those of main aerial axes basal to onset of branches erect, appressed to stem, ensheathing and hiding much or all of the stem, fragile, hyaline, incubously inserted, deeply concave-cucullate, 650–750 µm wide × 620–680 µm long, ovate, the apices narrow, (3)4-dentate-lobulate to 0.1; lobes terminating in a single cell or a uniseriate row of 2(3) cells, the lobe cells ± uniform in size and with at most small trigones. Leaves of main aerial axes distal to onset of branches not sheathing the stem, obliquely spreading, more deeply lobed than the leaves below, the lobe cells differentiated: those of uniseriate row and cells immediately below conspicuously larger than those toward lobe base, the latter with bulging trigones. Primary branch leaves smaller, concave, broadly ovate and more broad-based than those of main aerial axis, the apices 3–4-lobulate. Secondary branch leaves smaller than those of primary branches, the apex 2–3-dentate-lobulate. Tertiary branch leaves smaller than those of secondary branches, the apex short-bifid. Cells in median sector of main aerial axes leaves basal to onset of branches somewhat elongated, ± thin-walled, with minute trigones; cells in median sector of main aerial axes leaves distal to onset of branches subisodiametric or at most slightly elongated, firm-walled, with distinct trigones; surface striate-papillose. Oil-bodies totally absent. Underleaves similar to leaves of same shoot-sector except a little smaller and occasionally with one tooth fewer, the underleaves of ultimate branches bidentate-lobulate. Asexual reproduction lacking. Fungal partner an ascomycete.
Dioecious. Androecia on short, abbreviated, ventral- and lateral-intercalary branches from leafless bases of main aerial axes, the androecia spicate, whitish, variable, sometimes appearing to cease growth and then compact and bud-like to vermiform, but at other times proliferating vegetatively with the production of several small, sterile, scale-like leaves prior to the formation of a new androecium; bracts strongly ventricose-cucullate, the apex retuse to bidentate; antheridia usually 1 (at times 2) per bract, the stalk variable, uniseriate throughout or locally with 1 or a few biseriate tiers; bracteoles lacking antheridia. Gynoecia on reduced, highly abbreviated ventral-intercalary branches, the gynoecia strongly dorsally assurgent and becoming parallel or nearly so with upright leafy shoots, slender throughout and not swollen and rhizoidous at base; bracts in 4 series that all closely ensheath the gynoecium (including the mature perianth), the bracts concave, appearing membranous and like onionskin, those of second and third series (from base) often narrowed toward a 2–3-lobulate apex, the gynoecium also with a few scale-like bractlets at base; bracts and bracteole of innermost series identical or nearly so, firmly attached, erect, mutually connivent, together tube-like and tightly ensheathing the lower sector of the perianth, deeply concave-canaliculate, long-elliptic-sublinear, the apices broadly rounded, the apical and subapical cells thin-walled and distinctly striate-papillose, the apex with 4 rounded projections (lobules) barely perceptible; lamina cells dimorphic, those of a broad median field ± rectangular, with walls strongly thickened and red-brown, the surface striolate, those of margin and submargin irregular in shape, with walls thin and pale yellow-brown, the surface smooth or faintly striate-papillose, the marginal cells variable in shape, often long and narrow, the apical or free end of marginal cells often divergent and forming a crenulation, the margins otherwise with a few slime papillae. Perianth long-emergent, markedly slender and elongate-fusiform (to 9× longer than wide), terete in basal and median sectors, the distal sector obscurely trigonous, pluriplicate, the perianth strongly narrowed, contracted and ± pointed toward the apex; mouth shallowly lobulate, the cells thin-walled, rather elongated, laterally free for typically less than 0.5 the cell length but typically free for only very short distances, the mouth thus crenulate-denticulate, the cells at the mouth and those immediately below mouth distinctly striate-papillose; perianth 3(locally 4)-stratose in basal portion.
Seta with 9 rows of very large, firm-walled, outer cells (each with their free face bulging), surrounding an inner core of 28–32 much smaller cells. Capsule long-linear, with spiral dehiscence, the valves spirally twisted, long-linear and strap-shaped, the wall 38–46 µm thick, of 3–4 (locally 5) layers, the outer layer subequal to the combined inner layers, or slightly less thick, the exposed wall firm; outer layer of cells in tiers, rather regularly rectangular, with two-phase development, the longitudinal walls with well-defined, weakly sinuous, sheet-like thickenings and, sporadically, a few ill-defined nodule-like thickenings alternating with walls that are devoid of thickenings, the transverse walls devoid of thickenings; intermediate layer(s) in cross section thickened in the corners; innermost layer of cells ± tiered, rather regularly, narrowly and markedly long-rectangular; semiannular bands common, rather close, usually complete.
Spores 11.5–14.4 µm in diam., pale yellow-brown, with rather close granular-finely papillose markings and short vermiculae; spore:elater diam. ratio 1–1.2:1. Elaters rigid, many nearly perfectly straight, 10.6–12.5 µm wide, bispiral to tips, the spirals closely wound, notably wide, 4.8–6.2 µm wide.
The genus is monotypic.
References: Engel and Braggins (2005); Herzog (1951 sub Dendrolembidium); Schuster (1963b, 1980a, 2000a).
