Montana Field Guide

Plants: Pleurocarpous, growing in dense (FNA 2014) or slender mats (Crum and Anderson et al. 1981), pale green (FNA 2014) to brilliant green, green with yellow tones, or golden (Crum and Anderson et al. 1981), shiny. Stems creeping, to 20 mm, typically with leaves strongly flattened into one plane, or seldom appressed and overlapping, giving the stem a catkin-like appearance; pseudoparaphyllia wanting (FNA 2014).

Leaves: Overlapping or seldom remotely spaced, similar in wet and dry conditions, upright or spreading, occasionally noticeably turned to one side with tips directed toward the substratum, not symmetrical, not pleated, the blade plane or frequently a little wavy, to 2.6 mm in length and to 1.2 mm in width, egg-shaped and somewhat oblong to lance-shaped with ovate tendencies, gradually narrowing to the slender acumen; base extending down the stem, the decurrencies triangular (FNA 2014), but occasionally bulging or ear-like (Crum and Anderson et al. 1981); leaf edges flat or frequently a slender portion curved back and downward for much of the leaf length (not quite to the apex), smooth or occasionally with a few fine saw-teeth at the leaf tip; costa paired, scarcely exceeding the leaf bottom, with one division seldom reaching about halfway up the leaf, or costa absent. Branch leaves akin to stem leaves (FNA 2014).

Leaf Cells: Cells of the lamina smooth; basal cells of the lamina with walls pitted (Lawton 1971), wider and not as long as the medial cells; medial cells linear or linear and very narrowly diamond-shaped, sometimes slightly bent, usually longer than the apical cells, containing a lot of chlorophyll; alar cells oblong, arranged in up to 5 longitudinal rows and ending in a single cell at the bottom (FNA 2014).

Fruit ripens in summer (FNA 2014).

Plagiothecium laetum is generally smaller than the similar Plagiothecium denticulatum. P. denticulatum has leaves from 1.5-4 mm in length rather than 0.7-2.6 mm, wider medial cells, decurrencies often oval in shape and usually containing some oval-shaped cells rather than decurrencies deltoid with oblong cells, and capsules ridged rather than smooth when dry (FNA 2014).

Typically in evergreen woods, frequently in somewhat dry places, often on precipitous banks, not as frequent on tree bottoms, decaying wood, or soil and humus on top of boulders and shelves of bluffs (Crum and Anderson et al. 1981). Occurring from lowlands to 10,170 feet elevation (FNA 2014), most often above 2300 feet (Lawton 1971).

Autoicous, typically producing sporophytes. Perigonia and perichaetia numerous at stem bottoms. Seta 10-16 mm tall, spiraled, smooth, somewhat brown or sometimes red. Capsule upright to nodding, bowed or not, in a range of brown shades when well-developed, to 2 mm in length (FNA 2014), not shrunken below the opening when dry (Crum and Anderson et al. 1981), smooth, or the neck seldom creased in bowed forms; operculum to 0.8 mm, cone-shaped or with a short beak; exostome teeth with fine, transverse ridges below on the outer surface and papillae above; endostome processes keeled; cilia 1 or grouped in 2s or 3s, occasionally lacking (FNA 2014), knobby (Crum and Anderson et al. 1981). Calyptra draping hood-like, hairless, falling away easily (FNA 2014).

Specialized vegetative reproduction via 3- to 6-celled gemmae at the leaf junctures, typically present (FNA 2014).