Lejeunea schusteri

Detailed description

Plants corticolous, sterile, forming flat, closely adnate patches, extensively denuded of leaves, yellow-green, small (leafy shoots 500-600 µm wide, on branches narrower and 350-450 µm broad), freely but irregularly branched, forming thin,pure patches. Branches all thecal, Lejeunea type. Stems weak, rather fragile 65-74 µm broad, formed of 7 rows of essentially leptodermous, slightly inflated, large cortical cells (ventral merophytes 2 cell-rows broad; cells in surface view c.15-18(-20) x 32-50 µm); medullary cells slightly smaller, leptodermous, in 3 rows. Leafy shoots with contiguous but hardly imbricate lobes; lobes flat to very weakly convex c.250-265 x 315-33 µm, ovate, moderately narrowed to the narrowly rounded apices; lobe margins entire, not crenulate. Leaves di- to rather polymorphic; most on main stems, with inflated lobules, but even main stem in part, branches in large part, with reduced, often few-celled or vestigial lobules; inflated lobules about 0.34-0.4 in length and under 0.25 area of lobes, strongly, diagnostically inflated and tumid in aspect; keel rather convex, the cells bounding it convex but not strongly inflated; cells of free margins involute, usually 4(-5) below apical tooth; apical tooth erect, rounded, abbreviated and never hooked; larger lobules c.110 x 125 µm from keel base to apex of apical tooth. Reduced lobules usually on;ly 5-6-celled, with a blunt apical tooth usually formed by a single cell (+ ephemeral slime papilla). Underleaves ovate to subrotundate in outline, remote, small (to 105-115 x 115-135(-155) µm) the lobes erect, acute ending in a single not or slightly elongated cell; lobes usually 3-4 cells broad at the base; lateral margins convex but neither armed or angulate; rhizoid-initial field usually few-celled, obscure; sinus broadly V- to U-shaped, the base rounded; disc, to rhizoid-initials 2-3 cells high. Rhizoids usually lacking on mature shoots. Cells smooth, very weakly firm-walled or almost leptodermous, trigones vestigial or absent. Cells of lobe apices, marginally, rather small (11-15, 15-20 µm), in apices ranging into middle of leaf cells, variable, from 14-18 x 17-21 µm, up to 20-25 x 20-28 µm; in leaf base cells variable but much larger, leptodermous, 21-25 x 30-38 µm up to 25-28 x (35-)40-50 µm. Asexual reproduction via caducous leaves, resulting in the stems and branches mostly extensively denuded.