Leptotrichum gracile Mitten, Hooker’s J. Bot. Kew Gard. Misc. 3: 353. 1851; L. crispatissimum Müller Hal.; Ditrichum crispatissimum (Müller Hal.) Paris; D. giganteum R. S. Williams

Plants in tufts, yellowish brown to dark green, often shiny. Stems very variable in length, to 7 cm or more, simple or with relatively few branches; loosely compacted and then sparsely tomentose, or closely compact and rather densely tomentose. Leaves often ± falcate, slightly or not flexuose, subula of leaves often spirally twisted together, 4-7 mm, tapering ± gradually from an elongate ovate sheathing base to a long subula, lamina 1-stratose proximally, often 2-stratose distally in the subula; margins spinulose-denticulate in distal part of the subula or sometimes ± entire, often 2-stratose distally; costa occupying ¹/4-¹/3 width of leaf base, weakly abaxially convex, with poorly developed stereid bands abaxially and adaxially; cells of the subula and distal part of leaf base short, isodiametric to rhomboid to short rectangular, those of the leaf base becoming elongate, rectangular, with ± nodulose longitudinal walls, particularly near the costa, cells of the basal margins narrower. Specialized asexual reproduction unknown. Sexual condition dioicous; sporophytes rare; male plants slightly smaller than rarer female plants. Seta dark reddish brown, to 2.5 cm, ± flexuose. Capsule erect and symmetric to slightly inclined, dark brown, ± cylindric, 1.5-2 mm; operculum high-conic to conic-rostrate, to about 1 mm; peristome teeth about 400 µm, pale, 2-fid, divided to near base, densely papillose, fragile. Spores 12-15 µm, finely papillose.

Capsules rarely produced, mature summer (Jul). Soil, rocks; moderate to high elevations (to 4000 m); Greenland; B.C., Nfld. and Labr., N.W.T., Nunavut, Ont., Que.; Alaska, Colo., Minn., Mont., Wyo.; Mexico; Central America (Guatemala, El Salvador); South America (Colombia); Europe; Asia (Japan, Taiwan); Pacific Islands (New Guinea, New Zealand).

B. H. Allen (1994) included Ditrichum crispatissimum and D. giganteum as synonyms of D. gracile, an interpretation we have followed here. As with D. flexicaule, a detailed molecular analysis of this and related taxa may help considerably in ascertaining taxonomic affinities.