Hygrolembidium R.M.Schust.
Lembidium subg. Isodictyon Herzog, Ark. Bot. N.S. 1: 479. 1952 (1951), p. p.
Hygrolembidium R.M.Schust., J. Hattori Bot. Lab. 26: 277. 1963.
Type: Hygrolembidium stereophyllum (Herzog) R.M.Schust. (≡Lembidium stereophyllum Herzog)
Plants isophyllous to clearly anisophyllous, erect, clear green (without ability to develop secondary pigmentation), translucent or opaque. Branching exclusively intercalary, from axils of both leaves and underleaves, the leafy branches erect, straight; stolons generally freely developed, prostrate, freely branched, long, slender. Stem soft and ± fleshy, without a hyalodermis; cortical cells thin- or feebly thick-walled, averaging smaller than medullary cells (in ours); medullary cells leptodermous (in ours). Rhizoids of leafy branches issuing from basal cells of underleaves (and sometimes also of leaf) or from stem at immediate base of foliar tissue; rhizoids more regularly produced on stolons. Leaves concave to cupulate, commonly fleshy, at least the basal area 2–7-stratose, the insertion transverse to distinctly succubous; apex broadly rounded to retuse or incised, unlobed. Cells of leaf apices sometimes equally thick-walled, but at least in median and basal sectors of leaves (areas of 2 or more strata) leptodermous and without trace of trigones, the cells not enlarged; surface (at least of marginal and subapical cells) often ± papillose; median and basal, chlorophyllous cells with small, inconspicuous, glistening oil-bodies 1–2(3) per cell in isolated epidermal cells, the oil-bodies absent in many (in Hygrolembidium rigidum in essentially all) cells, some hypodermal cells with 3–9 similar, small, few-segmented oil-bodies. Underleaves distinct, ranging from 0.1–0.9 area of lateral leaves; apex undivided and crenulate to retuse to shallowly bifid; lamina margins feebly dentate. Asexual reproduction lacking.
Dioecious. Androecial plants often much smaller than ♀ plants; androecial branches either lateral- or ventral-intercalary in origin, spicate, sometimes proliferating vegetatively distally but never with vegetative leaves basal to androecium on a branch; bracts much smaller than leaves, very strongly saccate, bearing 1–4 antheridia each; antheridia with stalk 2–4(or more)-seriate; bracteolar antheridia lacking (except Hygrolembidium australe, where occasional). Gynoecia on short, abbreviated, intercalary branches lacking normal leaves, the branches either from axils of lateral leaves, or from axils of underleaves; bracts inserted on a broad base, the apex grading from entire and merely with slime papillae to 2–4-dentate-lobulate to distinctly bifid; lamina margins dentate to ciliate or entire; bracteole identical or nearly so to bracts, or slightly smaller. Perianth 3(4)-gonous at least above (occasionally cylindrical throughout in H. acrocladum), pluriplicate distally, contracted to the crenulate to lobulate mouth; perianth 2–5-stratose at base thinning to unistratose toward mouth.
Seta with 10–20 large, outer rows of cells surrounding numerous rows of moderately smaller internal cells. Capsule ellipsoidal to ovoid, the wall 3–5-stratose; outer layer of cells with one-phase development: with nodular thickenings on all or virtually all longitudinal radial walls (except Hygrolembidium rigidum where nodular thickenings weak or lacking), the transverse walls with nodular thickenings sparing to frequent; innermost layer with radial (vertical) bands nodular to spur-like in surface view, varyingly extended tangentially to form incomplete to complete, semiannular bands.
Spore wall with papillose to short-vermiculate markings.
Key to Species
The eight species of Hygrolembidium are chiefly Antarctic–subantarctic in range (one species, H. isophyllum R.M.Schust., occurs in Antarctica) and are present not only in continental areas (e.g., southernmost South America, H. isophyllum) but on most of the remote island regions (e.g., H. ventrosum (Mitt.) R.M.Schust. of Kerguelen, Crozet Island and Marion Island) including geologically recent, volcanic island groups. One species, H. andinum (Herzog) R.M.Schust., occurs in the Andes of central Chile and Venezuela and another, H. boschianum (Sande Lac.) R.M.Schust., occurs in Indo-Malaysia.
References: Schuster and Engel (1987b; mon.); Schuster (2000a).
