24.
Schistidium rivulare
(Bridel) Podpera, Beih. Bot. Centralbl. 28(2): 207. 1911.
Grimmia rivularis
Bridel, J. Bot. (Schrader) 1800(1): 276. 1801;
G. alpicola
var.
rivularis
(Bridel) Wahlenberg;
G
.
platyphylla
Mitten;
Schistidium platyphyllum
(Mitten) Persson;
S. rivulare
subsp.
latifolium
(J. E. Zetterstedt) Bremer;
S. submuticum
subsp.
arcticum
H. H. Blom
Plants
in open to compact, often extensive, tufts or mats, dark green, olivaceous, or brown, often yellow green distally, rarely nearly black.
Stems
1.2-10(-18) cm, central strand distinct.
Leaves
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.
Sexual condition
autoicous.
Capsule
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.
Spores
14-24 µm, granulose.
Capsules mature late spring to early summer. Wet to dry rocks in or along water courses and lakes, sometimes along seasonally irrigated ledges or cliffs, rarely on concrete or mineral soil; low to high elevations (0-4600 m); Greenland; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; South America; Eurasia; Africa; Atlantic Islands; Australia; Antarctic.
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).