5. Trichostomum recurvifolium (Taylor) R. H. Zander, Bull. Buffalo Soc. Nat. Sci. 32: 92. 1993.
Bryum recurvifolium Taylor, Ann. Mag. Nat. Hist. 11: 208. 1843; Bryoerythrophyllum recurvifolium (Taylor) R. H. Zander; Leptodontium recurvifolium (Taylor) Lindberg; Oxystegus recurvifolius (Taylor) R. H. Zander; Paraleptodontium recurvifolium (Taylor) D. G. Long
Stem rounded-pentagonal in section. Leaves flattened, long-ligulate or narrowly spathulate, distal margins plane, entire, bordered by 1-2 rows of smooth, more thick-walled cells; apex broadly acute to rounded, plane or concave; basal cells differentiated across leaf base as a U or V, not clearly running up margins, not distinctly enlarged submarginally; distal laminal cells pluripapillose with low papillae; mucro conic, of 3-4 cells.
Not fruiting in range of the flora. Wet, organic soil; B.C.; Alaska; Europe (w United Kingdom, Ireland).
Trichostomum recurvifolium, as may be seen in the multi-genus synonymy, is clearly difficult to place with confidence. A suite of gametophyte characters and color reactions to certain chemicals, however, indicate that it is near T. tenuirostre (R. H. Zander 1982b). It has many of the character states of broad- and notched-leaved forms of T. tenuirostre sometimes segregated as var. holtii (Braithwaite) Dixon, including yellow-green leaves, no stem central strand (variable in T. tenuirostre var. tenuirostre), presence of a hyalodermis, leaves oblong-ligulate, leaf apex reflexed, distal margins dentate, and distal marginal cells forming a border of thick-walled cells. Trichostomum recurvifolium, however, differs in the somewhat longer leaf base, sharp distal marginal teeth, which have conic lumens instead of elliptic, distal laminal cells rather thick-walled, and the cells of the distal marginal row are evenly distributed and quadrate to rhomboidal, not crowded and elliptic. The northwestern Europe to northwestern North America disjunctive distribution of T. recurvifolium is characteristic of a group of species apparently restricted to hyperoceanic climates. This species is found on Adak Island in the Aleutian Islands.