Plagiomnium cuspidatum
Plagiomnium medium
baby tooth moss, tooth plagiomnium moss, woods leafy moss, woodsy mnium
alpine thyme-moss, common leafy moss, greater tooth moss, intermediate plagiomnium moss, medium plagiomnium moss
dark green or yellow-green, contorted when dry, flat when moist, obovate, ± diamond-shaped or occasionally elliptic, 3–5 mm;
base broadly long-decurrent;
margins toothed from about mid leaf to apex, teeth sharp, of 1 (or 2) cells;
apex acute or acuminate, long-cuspidate, cusp sometimes toothed;
costa percurrent or excurrent;
medial laminal cells short-elongate or ± isodiametric, 20–30(–40) µm, slightly smaller near margins, occasionally in longitudinal rows, rarely in diagonal rows, strongly collenchymatous, walls not pitted;
marginal cells linear, in 2–4(–5) rows.
green or yellow-green, crisped and contorted when dry, flat when moist, elliptic, broadly elliptic, or sometimes obovate or oblong, (3.5–)4–7(–10) mm;
base long-decurrent;
margins toothed to near base, teeth sharp or occasionally blunt, of 1–2(–3) cells;
apex obtuse, rounded, acute, acuminate, or rarely retuse, mucronate or cuspidate, cusp sometimes toothed;
costa percurrent or excurrent;
medial laminal cells usually elongate, short-elongate, or occasionally ± isodiametric, (35–)50–65(–85) µm, less than 1/2 size near margins, in longitudinal or diagonal rows, collenchymatous, walls pitted;
marginal cells linear, in 2–4 rows.
single, yellow, brown, or sometimes reddish, 2–3 cm.
(1–)3(–7), yellow to reddish or orange with age, 2–5 cm.
synoicous.
synoicous.
pendent, ovoid or cylindric, 2–3.5 mm, neck not distinct;
operculum conic-apiculate.
pendent, oblong, cylindric, or narrow-ovoid, 3–4.5 mm, neck not distinct;
operculum conic-apiculate.
18–31 µm.
20–36 µm.
stems 1–2(–3.5) cm, not dendroid;
sterile stems to 7 cm.
stems 2–4 cm, not dendroid;
sterile stems to 8 cm.
Plagiomnium cuspidatum
Plagiomnium medium
Plagiomnium cuspidatum, P. drummondii, and P. floridanum are the only North American species of the genus that consistently have well-developed, sharp teeth restricted to the distal portions of the leaf margins. Plagiomnium ellipticum and P. rostratum often have leaves that are toothed only distally, but the teeth are small and mostly blunt, and the leaves are never obovate. Plagiomnium cuspidatum has larger leaves and larger, less collenchymatous laminal cells than P. drummondii and P. floridanum. The thinner cell walls and larger cells of P. drummondii give it a distinctly more translucent aspect than P. cuspidatum and P. floridanum.
In addition to the morphological characters in the key, Plagiomnium cuspidatum is separated from the closely allied P. floridanum by sexual condition, ploidy level, and ecology (R. Wyatt and I. J. Odrzykoski 2012). Plagiomnium cuspidatum is synoicous and diploid, with a chromosome count of n = 12, whereas P. floridanum is dioicous and haploid, with a chromosome count of n = 6. Although Plagiomnium cuspidatum exhibits a relatively broad ecological amplitude, P. floridanum shows a preference for soils associated with limestone.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Plagiomnium medium has most often been confused with 2. P. ciliare and 7. P. insigne; see the discussions of those species. The considerable morphological variation within P. medium may also reflect confusion with at least one undescribed species. One British Columbian collection that closely resembles P. medium is dioicous and has larger leaves and laminal cells. The leaf marginal teeth in P. medium are often hooked forward when composed of multiple cells.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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