Schistidium apocarpum
Schistidium rivulare
schistidium moss
river grimmia, river schistidium, streamside schistidium moss
1.2–12 cm, central strand weak or absent.
1.2–10(–18) cm, central strand distinct.
erect or curved, rarely (falcate-) secund when dry, ovate-lanceolate, sharply keeled distally, (1.3–)1.7–2.5(–3.2) mm, 1-stratose or rarely 2-stratose in striae distally;
margins usually recurved throughout or to just before the apex, usually denticulate distally, 1 or 2-stratose;
apices acute or sub-obtuse;
costa percurrent or excurrent as a smooth or weakly denticulate, occasionally decurrent awn, abaxial surface often papillose;
basal marginal cells usually quadrate;
distal laminal cells mostly short-rectangular, 8–10 µm wide, smooth, sinuose.
erect, often curved towards stem when dry and somewhat imbricate, sometimes secund, often slightly contorted when dry, ovate-lanceolate to ovate-triangular, keeled or concave proximally, keeled distally, 1.2–3.2 mm, 1-stratose, occasionally with 2-stratose striae or patches distally;
margins usually recurved to past mid leaf, sometimes to near apex, rarely plane, denticulate or smooth distally, 1- or 2-stratose, rarely 3-stratose, often in more than one row;
apices acute or obtuse, sometimes ending in a series of pellucid cells;
costa sub-percurrent or percurrent, sometimes as a short, smooth or weakly denticulate awn, smooth;
basal marginal cells mostly quadrate;
distal laminal cells angular, isodiametric or short-rectangular, 7–9(–11) µm, smooth, slightly sinuose.
autoicous.
autoicous.
dark red or brown, short-cylindric, 0.7–1.3 mm;
exothecial cells usually quadrate, sometimes mixed with short-elongate or oblate cells, thin-walled, usually trigonous;
stomata present;
peristome patent or erect, often twisted, 350–600(–700) µm, red, densely papillose, usually perforated.
red-brown or yellowish green, rarely almost black, short-cylindric, cupulate, or campanulate, 0.6–1.1 mm;
exothecial cells isodiametric, usually irregularly angular, or elongate, sometimes rounded, unevenly thickened or thick-walled, often trigonous;
rim usually darker than capsule wall;
stomata present;
peristome patent, squarrose-recurved, or revolute, 350–570 µm, dark red, densely papillose, usually weakly perforated.
11–14(–19) µm, granulose or smooth.
14–24 µm, granulose.
Schistidium apocarpum
Schistidium rivulare
Although H. H. Blom (1996) considered Schistidium apocarpum to be restricted in the flora area to the eastern portions of North America, it is more widespread and scattered across the continent. The denticulate leaf margins, papillose abaxial costal surface, short-cylindrical capsules, and the thin-walled, often evenly quadrate exothecial cells are distinguishing characters. The long peristome teeth are also useful in identifying S. apocarpum. In good condition the peristome can only be confused with that of S. trichodon, which differs in the darker, often black color of its plants, the peristome teeth often forming a dome, and the cylindrical capsules that retain the columella.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Schistidium rivulare is the most variable and widely distributed species of the genus in North America. A myriad of forms have been recognized at various taxonomic levels, but none more than the smaller and more triangular-leaved form (e.g., S. platyphyllum and S. rivulare subsp. latifolium). H. H. Blom (1998) separated S. platyphyllum mainly using the thickness and shape of the exothecial cells, with S. rivulare having short, thick-walled, irregular cells and S. platyphyllum having more or less regular, thin-walled, and elongate cells. These features, however, at least within North American specimens, vary from place to place and sometimes between capsules in the same collection. Other characters used to separate the taxa, such as the more keeled leaves of S. rivulare and its absence of an awn, also are variable. Differences between S. rivulare and the closely related S. subjulaceum are discussed under the latter species. Schistidium rivulare is sometimes confused with S. agassizii, also found along watercourses, but it is readily separated by its more ovate, distally keeled leaves with recurved margins. Schistidium alpicola Hedwig is a name that has been frequently applied to this complex, but is no longer useful (see Blom for further discussion).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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