Sciuro-hypnum plumosum
Sciuro-hypnum uncinifolium
leaves erect-appressed to erect, densely to moderately densely imbricate, ovate-lanceolate to ovate, concave, not plicate, 1.4–2 × 0.4–1 mm;
base narrowly decurrent;
margins plane or recurved just beyond insertion, serrulate;
apex short-acuminate;
costa to 35–65% leaf length, broad proximally, conspicuously narrowing distally, terminal spine absent or small;
alar cells similar to juxtacostal cells or slightly larger, to 15 µm wide, walls moderately thick, region opaque;
laminal cells elongate, 30–75(–90) × 5–9 µm;
basal cells short-ovate, region in 3–7 rows across base.
leaves appressed at base, wide-spreading falcate-secund to reflexed, closely imbricate, ovate or triangular-ovate, weakly concave, not plicate, 0.8–1.1 × 0.4–0.5 mm;
base decurrent;
margins plane or recurved below broadest point of leaf, serrulate;
apex gradually or abruptly narrowly acuminate;
costa to 90–100% leaf length, moderately strong, terminal spine absent;
alar cells similar to juxtacostal cells;
laminal cells elongate, 30–50 × 5–8 µm;
basal cells subquadrate, short-ovate, relatively small, region in 7–10 rows, opaque across base.
with margins more strongly serrate.
similar.
cherry red, 1.2–2(–2.4) cm, rough, sometimes weakly so.
autoicous.
autoicous.
slightly to moderately inclined, reddish, ovate, slightly curved dorsally, 1.3–2 mm.
13–19 µm.
unknown in North America.
Sciuro-hypnum plumosum
Sciuro-hypnum uncinifolium
Plants of Sciuro-hypnum plumosum from drier habitats have narrower, straight leaves, while northern populations from semipermanently wet rocks sometimes have strongly falcate leaves. The transition between these extremes does not allow for satisfactory segregation of these forms. Although S. plumosum is extremely variable, it is usually easy to recognize with stereomicroscope or hand lens. The sometimes variegated color patterning with ferruginous or even reddish spots is characteristic. However, in evenly colored plants, the leaves are very strict and very broadly channeled; the narrowing of the costa in the proximal third of leaf and the opaque cells across the leaf base are also characteristic. Brachythecium acuminatum may sometimes be confused with S. plumosum, as both have more or less isodiametric cells across the leaf base; however, the former species has larger and more transparent basal cells and its leaves usually have distinct submarginal plicae. Sciuro-hypnum oedipodium also may have an extensive opaque area in leaf corners, but never across the whole leaf base. In some cases, especially in wetter habitats, cells in the leaf corners of S. plumosum can be enlarged and pellucid, but if so, small opaque cells remain between them and laminal cells.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Sciuro-hypnum uncinifolium has long been considered a Japanese endemic, but recently it was found in Russia in Kamchatka and in the Kuril Islands (I. V. Czernjadieva and M. S. Ignatov 2006; V. Y. Cherdantseva et al. 2006) and also in islands near Alaska and in the Alaskan peninsula (M. S. Ignatov 2007), so it is to be expected in the Aleutian Islands. Sciuro-hypnum uncinifolium is easily recognized by its narrow shoots, appressed leaf bases, and leaves rigidly reflexed, with squarrose to falcate-secund acumina. This species combines the characters of S. reflexum (leaf shape and reflexed acumen) and S. populeum (opaque cells across the leaf base). From molecular phylogenetic analyses by Ignatov and I. A. Milyutina (2007b), it is more closely related to the latter species. Despite its autoicous condition, sporophytes are rare in this species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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