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.)

Genera 20–30, species 100–150 (20 genera, 57 species in the flora).

Amblystegiaceae as here circumscribed include several genera or species groups that may not or are even unlikely to belong to this family in a strict sense. These include Calliergonella, Campylophyllum, Conardia, most of Hygrohypnum, Limbella, Platydictya jungermannioides, Platylomella, Sanionia, and Tomentypnum. The genus Amblystegium is here understood in a broad sense, including Hygroamblystegium but excluding Serpoleskea (here treated in Platydictya).

Amblystegiaceae is sometimes confused with other pleurocarpous families, such as Brachytheciaceae and Plagiotheciaceae. Most Brachytheciaceae and Plagiotheciaceae differ from Amblystegiaceae in their non-plicate and often recurved, rather than plicate and erect, inner perichaetial leaves (in species with horizontal capsules). In Brachytheciaceae, horizontal capsules are swollen rather than cylindric, the stomata round-pored rather than long-pored, and the exostome base is mostly red or brown-red rather than yellow-brown. The exostome teeth borders are gradually narrowed upwards rather than suddenly widened where the exterior pattern of the teeth changes from cross striolate to papillose, the endostome segments are widely rather than narrowly perforate, and the spores mature in winter rather than summer in temperate areas. Plagiotheciaceae members have pale whitish yellow exostomes and differ from Amblystegiaceae in several diagnostic gametophyte features, including rhizoid position and ornamentation, and branching mode (see 4. Platydictya treatment).

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