Pseudocrossidium crinitum
Pseudocrossidium obtusulum
pseudocrossidium moss
leaves ovate to short-lanceolate, 1.5–1.9 mm including the awn, distal margins strongly recurved to once revolute;
apex rounded-obtuse below the awn;
costa ending in a short awn, adaxial surface of costa at mid leaf concave, with 4 guide cells;
distal laminal cells 12–15 µm wide, 1:1.
leaves ovate to ovate-deltoid, 0.7–1.2 mm, distal margins once to almost twice-revolute;
apex broadly acute;
costa ending in an apiculus, adaxial surface of costa at mid leaf convex, with 2–3 guide cells;
distal laminal cells 10–13 µm wide, 1:1.
1–2 cm.
1–2 mm, peristome of 32 linear, yellow teeth, straight or twisted counterclockwise a half turn, operculum conic-rostrate.
yellow, essentially smooth, 8–12 µm.
asexual reproduction absent.
asexual reproduction occasionally present as spheric to clavate gemmae, 40–50 µm, borne on the adaxial surface of the costa, or as rhizoid-borne brood bodies.
leaves not or weakly differentiated.
Pseudocrossidium crinitum
Pseudocrossidium obtusulum
Pseudocrossidium crinitum, when the awn is short, can be distinguished from P. replicatum (forms of which may have strongly mucronate leaf apices) by the large area of differentiated parenchymatous cells on the abaxial lateral surface of the costa on both sides adjacent to the laminal insertion on the costa, easily seen in section at mid leaf and often deep yellow in color, appearing as a row of ocelli; the leaf marginal cells are very thin-walled. This essentially southern species reaches its northern range extension in western United States E. B. Bartram 1924; R. H. Zander 1993). An exceptionally robust collection of P. crinitum from Mexico (Puebla, Azumbilla, Zander 4899, BUF) has two layers of guide cells in the costa, but this is very unusual.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Pseudocrossidium obtusulum differs from P. revolutum (Bridel) R. H. Zander of Europe and Africa (absent in North America), by not or weakly differentiated perichaetial leaves, and cauline leaves ovate to deltoid, broadly acute, once-revolute, and revolute only in distal 2/3 of leaf. Discussions of the morphology and distribution of P. obtusulum in the New World have been published by G. R. Brassard (1971), P. M. Eckel et al. (1996), B. C. Tan et al. (1981), and R. H. Zander (1979). It has been collected as subfossil in the Yukon (J. A. Janssens and R. H. Zander 1980) and Vermont (N. G. Miller 1987). Fruiting material has been collected in Greenland—the peristome generally comes off with the operculum. A collection from Oregon (McIntosh 4939, UBC) has gemmae on the adaxial surface of the costa (as does P. revolutum). Didymodon brachyphyllus and D. nevadensis have somewhat the same appearance, but have merely strongly recurved distal laminal margins and an indistinct apex. This species has been collected widely in Alaska (B. M. Murray 1992), California (D. H. Norris and J. R. Shevock 2004), and Washington (T. T. McIntosh, unpubl.).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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