Adelanthus Mitt.
Adelanthus Mitt., J. Proc. Linn. Soc., Bot. 7: 243. 1864, nom. cons.
Type: A. falcatus (Hook.) Mitt.
Calyptrocolea R.M.Schust., Rev. Bryol. Lichénol. 34: 685. 1967 (1966).
Type: C. gemmipara R.M.Schust.
Type: Adelanthus falcatus (Hook.) Mitt. (≡Jungermannia falcata Hook.)
Plants slender, rigid and wiry yet flexuous, deep green to ± deep brown to black with maturation, nitid, small to medium, to 2.4 mm wide; leafy shoots stiffly erect, arising from a ± intricate system of branching, rhizomatous axes. Branching normally exclusively intercalary, the branches normally arising ventrally or from ventral leaf angles low down on leafy shoots, never clearly axillary, either abruptly phototropic after their origin and then becoming leafy, or geotropic and then forming stoloniform axes commonly occurring just beyond point of origin of a leafy branch, the leafy and stoloniform axes mostly at 180° to each other; erect leafy axes usually unbranched above, rarely and sporadically with a Frullania -type branch distally. Stems rigid and wiry, usually fuscous pigmented and darker than the leaves, with cortical cells persistent and not collapsing (a hyaloderm lacking), in surface view strongly elongated (4–10:1), in cross section with a well-defined, (1)2–3-stratose cortex of small cells with extremely thick walls and reduced lumina. Rhizoids almost exclusively confined to stoloniform axes. Leaves nitid, usually vertically or subvertically oriented, the dorsal leaf surface inclined or appressed to axis, erect to erect-spreading, scarcely to weakly concave, the mature ones suborbicular to asymmetrically ovate to ovate-reniform; margins usually denticulate to serrulate, occasionally entire, the apices never bidentate, the dorsal margin often clearly incurved, never deflexed. Cells (except marginal and submarginal ones) rather small, oblong (mostly 1.5–3:1), grading into a basal region of strongly elongated cells (to 3–6:1) and with a ± well-defined vitta differentiated, the median and basal cells serially oriented, the upper cells thin-walled to firm-walled and lacking distinct trigones, the elongated basal cells with walls evenly thick-walled but without distinct trigones, the lumina rounded at the angles; cells of marginal 2–4 (or more) rows often thick-walled, subquadrate to short-rectangular with long axes usually oriented radially, forming a ± distinct border. Oil-bodies 3–9 per median cell, finally papillose to irregularly botryoidal. Underleaves reduced to 1–2 cells or absent. Asexual reproduction by 1–2-celled, elliptical to ovoid, green gemmae, formed at shoot apices from reduced leaves and/or geotropic axes.
Androecia confined to basal, very short, ventral-intercalary branches, whitish; bracts in 4–6 pairs, small, imbricate, unlobed or emarginate; antheridia normally 1 per bract. Gynoecia confined to basal, very short, ventral-intercalary branches lacking vegetative leaves; bracts in 2–4 gradually larger series or the innermost at times smaller, the innermost series delicate, weakly or not chlorophyllous, the apices unlobed or ± 2–3-lobed, the margins toothed; shoot-calyptra massive, ovoid-cylindrical at maturity, green, fleshy, with polystratose wall, the unfertilized archegonia present to at least the middle; perianth wholly lacking (except sect. Pittieri).
Capsule ovoid to ellipsoidal, the wall 4–6-stratose; outer layer of cells with strongly developed nodular (radial) thickenings, mostly confined to alternating longitudinal walls; innermost layer of cells with well-developed complete to incomplete semiannular bands.
Spores granulate or with vermiculate, rarely anastomosing ridges; spore:elater diam. ratio 1.4–1.7:1. Elaters bispiral, the spirals close, rather wide.
Key to Species
A genus of 10 species. SectionCalyptrocolea (R.M.Schust.) Grolle has three species, including the closely related species pair Adelanthus tenuis J.J.Engel & Grolle of the Falkland Islands, Tierra del Fuego, southern South America and A. gemmiparus of our area. The third species (A. areomarginatus R.M.Schust.) is Andean. Two of the three species of sect. Lindenbergiani Grolle also are Austral. Adelanthus integerrimus Grolle is subantarctic (Crozet Island, South Georgia, Falkland Islands, Tierra del Fuego and southern South America) and A. lindenbergianus (Lehm.) Mitt. is amphi-Atlantic-temperate, occurring on Mascarene Island, Réunion, Madagascar, South Africa, East African mountains, Tristan da Cunha, Inaccessible Island, South Georgia, Falkland Islands, Tierra del Fuego, southern South America, Juan Fernandez, and the Andes north to Mexico, and is disjunct in western Ireland and NW Scotland. The third species (A. carabayensis (Mont.) Grolle) is Neotropical. SectionAdelanthus has two Australasian species, both occurring in our area. SectionPittieri Grolle has two species: A. pittieri (Steph.) Grolle of the high Andes and the mountains of Central America + Jamaica and A. squarrosus Grolle of Guyana (Mt. Roraima). The genus does not extend into tropical sectors of the Old World.
Adelanthus is also distinct from Pseudomarsupidium in several sterile gametophyte characters. Species usually develop gemmae; those of Pseudomarsupidium never. Plants of Adelanthus usually show a clear distinction between a fuscous to blackish stem and polished leaves; the stem has a 2–3-layered persistent cortex of strongly pigmented and greatly elongated cells with greatly reduced lumina vs. a weakly differentiated cortex formed of only moderately incrassate cells in Pseudomarsupidium. In Adelanthus the leaf shows strong regional cellular differentiation: the peripheral cells, in several rows, average small and subquadrate (1–1.2:1), grading into subapical and median cells that are rectangular to hexagonal-rectangular (to 3:1), grading into a basal field of narrowly rectangular cells (to 6:1). Except at the leaf margins, cells are mostly oriented in lines or arcs and are often locally tiered. All cells are basically non-collenchymatous, the walls evenly thickened, the lumina remaining angular. These differences are much less marked in A. gemmiparus. Also, Frullania -type branching is developed in some taxa (e.g., A. falcatus); in Pseudomarsupidium terminal branching is completely lacking.
Descriptions are adapted, with much modification, from Schuster (1967c).
References: Grolle (1972a, rev.; 2003); Hodgson (1970, rev.); Schuster (1967c; 2002a).
