Sciuro-hypnum populeum
Sciuro-hypnum hylotapetum
leaves erect-appressed to erect, closely imbricate, ovate-lanceolate, straight, weakly concave, not or indistinctly plicate, 1.2–1.9 × 0.4–0.6 mm;
base moderately broad-decurrent;
margins plane or recurved in places (more commonly proximally), serrulate to subentire;
apex gradually tapered, short-acuminate;
costa to 80–100% leaf length, moderately strong, terminal spine sometimes present;
alar cells similar to juxtacostal cells;
laminal cells elongate or sometimes rhomboidal, 25–80 × 5–8 µm;
basal cells subquadrate to quadrate, relatively small, region in 5 rows, opaque across base.
leaves patent, loosely arranged, broadly ovate, moderately concave, not plicate, 2.2–3.7 × 1.3–2 mm;
base narrowly short-decurrent;
margins plane or recurved below broadest point of leaf, slightly serrulate to subentire, serrulate to serrate in apex;
apex short-acuminate or apiculate;
costa to 40–65% leaf length, broad near base, then evenly narrow, sometimes 2-fid, terminal abaxial spine absent;
alar cells larger than juxtacostal cells, to 40–75 × 20–27 µm, walls thin, region indistinctly delimited;
laminal cells linear, (80–)110–155(–185) × 7–13 µm;
basal cells shorter, broader than laminal cells, region in 2–4 rows.
with abaxial costa surface somewhat serrate.
with margins more serrulate to serrate;
apex more gradually acuminate.
reddish, 0.8–1.5 cm, rough, sometimes slightly so.
chestnut to purple-red, 1–3 cm, rough.
autoicous.
dioicous.
slightly to moderately inclined, reddish, ovate, slightly curved dorsally, 1–2 mm.
horizontal, reddish, oblong, curved, length variable, 1.5–2.5 mm.
12–16 µm.
12–20 µm.
Sciuro-hypnum populeum
Sciuro-hypnum hylotapetum
Sciuro-hypnum populeum is usually a lowland species, and the only exception is the population in Colorado at 2000 m (Boulder County, Bear Mt., W. A. Weber & R. C. Wittmann B-112127, COLO). H. A. Crum and L. E. Anderson (1981) noticed that, unlike in Europe, this species does not grow on tree trunks in North America, although it has occasionally been collected on tree bases in forests. Sciuro-hypnum populeum can be recognized by its combination of percurrent costa with opaque basal cells, unique among North American Brachytheciaceae. Sometimes it has been confused with Homalothecium species with costae masked by their characteristic laminal plications, and appearing percurrent. Brachythecium acuminatum and S. plumosum are similar to S. populeum in having short and more or less uniform cells across the leaf base, but the costa in these species disappears well below the apex. Sciuro-hypnum populeum may develop rather broad stem leaves with bigger basal cells in relatively wet conditions, as has S. reflexum. However, the more gradual tapering of the leaves is diagnostic.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The endemic Sciuro-hypnum hylotapetum has been reported from Alaska (W. C. Steere 1978) and California (D. H. Norris and J. R. Shevock 2004). The species is easy to identify by its robust stature, leaves longer than 3 mm, and light green to whitish color. The usually apiculate leaves and recurved leaf margins near the insertion are also diagnostic. The plants are strongly glossy; the leaves are broadest at 1/7 the leaf length. Sporophytes are rare.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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