Flora of North America species comparison

Platygyrium repens is one of the most ubiquitous pleurocarpous mosses in eastern North America. The species fruits infrequently in the northern reaches of its range and not at all in the southern portions. Brood branches are usually present and are rarely elongate and in such abundance that the plants dissolve into seemingly amorphous masses of slender branchlets. Although most specimens of P. repens can be identified easily, occasional sterile specimens lacking brood branchlets may defy certain identification. Homomallium adnatum sometimes has brood branchlets at its branch apices, and some sterile specimens may not be confidently distinguished from sterile specimens of P. repens. However, in H. adnatum the medial laminal cells are generally much shorter (rhombic or to 3–5:1) than those of P. repens, and foliose paraphyllia are sometimes present in the former but absent in P. repens. Erect branches bearing brood branchlets at their apices are also common in Leskeella nervosa, a more slender, dull, brownish, plant with narrow costate leaves, which co-occurs with P. repens in the northern reaches of its range.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 8 (2 in the flora).

Platygyrium has concave leaves with yellowish bases. The alar region has vertical rows of cells with conspicuously thick walls. Platygyrium is superficially similar to Homomallium and Pylaisia. Fruiting specimens of these three similar genera are easily distinguished; the capsules of Homomallium are curved and asymmetric, often strongly so, in contrast to the erect symmetric capsules of Platygyrium and Pylaisia. The long, slender, rather obliquely rostrate operculum of Platygyrium (conspicuous when dry) distinguishes it from Pylaisia, in which the operculum is only conic or with a short blunt rostrum. Platygyrium and Pylaisia commonly grow on xylic substrates but Homomallium typically occurs on rock. Dehiscent branchlets clustered at the branch apices are very common in Platygyrium, particularly P. repens, but such branchlets also occur infrequently in Homomallium. Also, the leaf margins of Platygyrium are usually recurved, sometimes strongly so, while those of Homomallium and Pylaisia are erect. Recurvature of the leaf margins is not always well defined in P. repens but is usually conspicuous in P. fuscoluteum.

(Discussion copyrighted by Flora of North America; reprinted with permission.)