28. LEPTODONTIUM          Plates 36– 37.

Leptodontium (C. Mόll.) Hampe ex Lindb., Φfv. K. Vet. Ak. Fφrh. 21: 227, 1864. Type: Leptodontium squarrosum (Hook.) Hampe in Lindb.

Sect. Leptodontium

Didymodon subg. Leptodontium (C. Mόll.) Lor., Bryol. Notizb. 18, 1865.

Trichostomum sect. Leptodontium C. Mόll., Syn. 1: 577, 1849.

Sect. Verecunda Zand., Bryologist 75: 230, 1972. Type: Leptodontium flexifolium (Dicks. ex With.) Hampe in Lindb.

Didymodon subg. Leptodon BSG, Bryol. Eur. 2: 2, 1851 (fasc. 46–47 Consp. 2: IV), p.p.

Sect. Crassicostata Zand., Bryologist 75: 256, 1972. Type: Leptodontium pungens (Mitt.) Kindb.

Sect. Coronopapillata Zand., Bryologist 75: 264, 1972. Type: Leptodontium longicaule Mitt.

Williamsia Broth., Nat. Pfl. 1(3): 1190, 1909, hom. illeg. non Merrill, 1908. Type: Williamsia tricolor Williams.

Williamsiella Britt., Bryologist 12: 62, 1909, nom. nov. for Williamsia Broth.

 

            Generally robust plants, in thick mats or short turf, greenish yellow- to orange-brown above, yellow- to red-brown below. Stems seldom to often branching, 1–5(–20) cm in length, transverse section rounded-pentagonal, central strand absent, outer cortex usually of thick-walled cells, hyalodermis often present, usually collapsed in mature parts of stem; axillary hairs of 6–16 cells, cells often bulging, with hyaline walls or basal 1–2 cells brownish; tomentum often present, red to brown, knotty or kinky. Leaves erect to spreading, twisted to contorted when dry, spreading to squarrose-recurved when wet, ovate- to long-lanceolate, occasionally lingulate or oblong, (1–)2–5(–8) mm in length, keeled above or channeled along costa, margins recurved in lower 1/3–3/4, rarely to near insertion, usually dentate in upper 1/3–1/2, rarely to near insertion, occasionally bordered above by 1–5 rows of less papillose, thick-walled cells; apex acute, occasionally rounded to narrowly obtuse; base commonly rectangular, often sheathing, basal margins sometimes long-decurrent; costa shortly excurrent, percurrent or ending 1–6(–15) cells below apex, superficial cells elongate both ventrally and dorsally, costal transverse section reniform, occasionally elliptical or semicircular, two stereid bands present, epidermis absent both ventrally and dorsally, guide cells 2–4 in 1 layer, hydroid strand absent; upper laminal cells subquadrate, mostly 11–15 ΅m in width, 1:1, walls thin or evenly to collenchymatously thickened, often trigonous, occasionally strongly bulging superficially; papillae variously simple, bifid, multifid, often hollow (oh- or cee-shaped in optical section), occasionally simple- or branching-columnar; basal cells generally strongly differentiated medially or across base, often sharply demarcated and hyaline, rectangular (occasionally somewhat inflated), slightly wider than upper cells, 2–5:1, walls thin to evenly or laterally thick-walled, occasionally porose. Propagula multicellular, clavate to obovate, borne on short stalks in leaf axils, occasionally on leaf apices or leafless branchlets. Flagellate branchlets occasionally present in axils. Usually dioicous, rarely autoicous or possibly rhizautoicous. Perichaetia terminal, inner leaves usually long-lanceolate, to 7–8 mm in length, usually convolute-sheathing, lower cells long-rhomboidal, porose or thin-walled. Perigonia terminal or lateral (as autoicous buds), or both lateral and terminal on antheridiate plants. Seta 0.3–3.0 cm in length, 1(–2) per perichaetium, twisted usually clockwise above; theca cylindrical, 2.0–3.5 mm in length, exothecial cells short-rectangular, moderately thick-walled; stomates absent or present at base of theca; annulus of 2–7 rows of yellowish or reddish vesiculose cells, persistent or irregularly deciduous; peristome teeth 16, linear, occasionally rudimentary (a preperistome rarely present), yellowish brown to reddish orange, smooth to deeply striate, usually 300–500 ΅m in length, of several articulations, straight, basal membrane absent or very low. Operculum conic to conic-rostrate, 0.5–1.0 mm in length, cells in straight rows. Calyptra cucullate, smooth, 2.5–4.0 mm in length. Spores homogeneous or occasionally heterogeneous, i.e., in one capsule half larger and chlorophyllose and half smaller andbrownish, weakly papillose, mostly ca. 17–20 ΅m in diameter. Laminal KOH color reaction usually strong, yellow or less often orange to yellowish orange, occasionally yellow with red blotches. Reported chromosome number n = 13.

            This is a large genus found mainly in tropical, mountainous areas of the world, especially characteristic of high elevation fog forests, growing on soil, acidic rock, trees and shrubs.

            The genus Leptodontium is superficially well distinguished by the robust size of the plants, squarrose-recurved and carinate leaves, sheathing leaf base, elongate and sheathing perichaetial leaves (Pl. 36, f. 9), and the straight peristome teeth (Pl. 36, f. 10), but there is significant variation in many of these characters among the species. More constant features include the absence of a stem central strand (Pl. 36, f. 2–3), absence of a differentiated epidermis over the costa (Pl. 36, f. 8), and smooth or striate peristome teeth (Pl. 36, f. 10). Although Leptodontium is, all in all, a surprisingly well-delimited genus (for the family), Leptodontiella and Streptotrichum are rather similar in morphology when sterile, and their descriptions and illustrations should be carefully studied to avoid confusion. These last two genera lack stomates in their capsules, as do many species of Leptodontium. Hollow papillae reported (Newton & Boyce 1987) as “mamillae” in British L. flexifolium are actually rather common in tropical collections of that species.

            A revision for the New World (Zander 1972) reviewed the nomenclatural history, morphology and geographic distribution of the genus in detail, including much discussion of extra-American species. Sloover (1987) provided a key to the tropical African species of the genus.

            Didymodon sect. Fallaces is rather similar in aspect to Leptodontium. Didymodon erosodenticulatus has many of the characteristics of L. viticulosoides (Pl. 37, f. 10–15), including reflexed, keeled leaves with serrate upper leaf margins and simple papillae, but differs significantly in the presence of a stem central strand, brownish basal cells of the axillary hairs, costal ventral epidermal layer present in at least some leaf sections, perichaetial leaves not strongly differentiated, and red-orange laminal KOH color reaction. Hymenostylium ((q.v.) has many of the characters of Leptodontium. The presence of upper laminal cell wall trigones in Hymenostylium and the related genus Reimersia, plus the keeled leaves, general absence of a dorsal costal epidermis and of a stem central strand are important characters indicating an ancestral link with Leptodontium, and this link is supported by the cladistic study. Trigones are variously present in L. wallisii (Peru, Hegewald 6948, BUF; Colombia, Van Cleef 249, BUF) and L. viticulosoides.

            Leptodontium stellatifolium of Brazil has somewhat the appearance of Barbula sect. Convolutae and has an unusual bright orange coloration of its basal cells, but may be retained in Leptodontium by its striate peristome teeth.

     Crum and Anderson (1981) recognized L. excelsum (Sull.) Brit. (given as a synonym of L. viticulosoides var. panamense [= var. sulphureum] by Zander 1972) as a good species endemic to the Appalachian Mountains of the southeastern United States, based largely on a uniformity of small size and flagellate appearance. Robust collections from Jackson Co., North Carolina (BUF), which they may not have seen, are quite like L. viticulosoides from Mexico, and their report of an autoicous sexual condition would require transference of this name to the synonymy of L. viticulosoides var. viticulosoides; the material available to me lacks perigonia. Actually, the var. sulphureum is commonly dimorphic (cf. Mexico, Oaxaca, Smith et al. 3028, TENN), the perigoniate plants with hair-like stems and distant leaves and the perichaetiate not flagellate.

     Leptodontium stoloniferum (Pl. 37, f. 7–9) has the appearance of species of Calymperaceae, but it differs in the shape of the laminal papillae, in the stalk bearing the propagula being branch-like (not a modified leaf), and the propagula with internal longitudinal cross walls (Calymperaceae apparently have only uniseriate cells in their propagula). A specimen from Ecuador (Steere 27591, BUF, NY) has centered, capituliform papillae, which places the species in sect. Coronopapillata.

     The anisosporous condition (heterogeneous spores, with two size classes) characteristic of the spores of L. viticulosoides var. viticulosoides (Anderson & Zander 1986) was also found, at least rarely, in L. wallisii; in one Bolivian collection (Cochabamba, Lewis 79–2217, F), about half the spores in a capsule were brown and collapsed, the other half green and turgid. Recognized in my (Zander 1972) revision, L. viticulosoides var. exasperatum is characterized by high, columnar upper laminal papillae and is variably isosporous or anisosporous in different collections. Two additional collections (Mexico, Bowers et al. 5252, 5264–f, both BUF and TENN) have capsules showing both conditions in the same collection; the latter specimen is clearly dioicous. Perhaps the lethal factors proposed by Mogensen (1978, 1981, cf. Andrews 1929, Wettstein 1928) in his discussion of false anisospory are the source of variation in spore size in Leptodontium; this should be investigated.

     Additional literature: Frahm (1973, 1986), Herzog (1932), Janssens and Zander (1980), Long (1982b), Newton and Boyce (1987), Schumacker and de Zuttere (1981), Sloover (1987), Zander (1982b, 1983d), Zander and Hegewald (1976), Zander & Vitt (1979).

     Number of accepted species: 39.

     Species examined: see revision (Zander 1972) of species in North, Central and South America, also L. aggregatum (NY), L. gemmascens (NY), L. hyalinum (FH), L. insolitum (FH), L. interruptum (FH), L. joannis-meyeri (NY), L. latifolium (H), L. paradoxicum (BUF), L. pumilum (US), L. styriacum (NY), L. taiwanense (US).

            New heterotypic synonymy: Leptodontium ramosum Crum & Richar ds = Leptodontium stoloniferum Zand.