Flora of North America species comparison

Strikingly rigid plants of Cratoneuron filicinum with extremely strong, often long-excurrent costae are sometimes found in streams or under heavily dripping water; these were sometimes recognized as Amblystegium tenax var. spinifolium in North America. Such plants have narrowly triangular or narrowly ovate-triangular leaves gradually narrowed to an acuminate or often obtuse point. Ordinary C. filicinum leaves are sometimes found in parts of such plants, or shoots on old plants of this kind may have a normal C. filicinum appearance. Molecular studies show that such plants likely represent habitat modifications and should therefore not be recognized taxonomically (L. Hedenäs 2011, 2012). Cratoneuron curvicaule (Juratzka) G. Roth was attributed to North America by H. A. Crum et al. (1973) as C. filicinum var. curvicaule (Juratzka) Mönkemeyer; the species has been considered a synonym of C. filicinum on several American web pages. However, as shown by Hedenäs (2003, 2011), this is a distinct species that differs both morphologically and molecularly from C. filicinum. The occurrence of C. curvicaule in North America has not been confirmed, and the only North American specimens referred to this species (H. G. Simmons 584 [in part] and 585, S) belong to C. filicinum.

(Discussion copyrighted by Flora of North America; reprinted with permission.)