Flora of North America species comparison

Calamagrostis rubescens grows at 50-2800 m, usually in open montane pine or aspen forests and parklands, infrequently in sagebrush steppes, chaparral, and meadows. It is primarily a species of interior western North America, although it reaches the Pacific coast in southern California. The distribution extends from central British Columbia and Alberta east to the Cypress Hills of eastern Alberta and the Pasquia and Cub hills of Saskatchewan, south to western California, Nevada, northeastern Utah, and central Colorado. It is considered threatened in Saskatchewan.

Calamagrostis rubescens is similar to C. koelerioides (p. 721). The two have traditionally been distinguished by the presence of hairs on the leaf collars of C. rubescens, and their absence from C. koelerioides; a more reliable differentiation is the shorter lemmas, glumes, and awns of C. rubescens. Calamagrostis rubescens and C. porteri (p. 721) appear to be closely related. They may be part of the general phenomenon of eastern and western vicariants.

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

Calamagrostis grows in cool-temperate regions and is especially diverse in mountainous regions. Its species grow in both moist and xeric habitats. There are about 100 species of Calamagrostis, if Deyeuxia Clarion ex P. Beauv. and Lachnagrostis are recognized as distinct from Calamagrostis. The latter two genera are often considered to be restricted to the Southern Hemisphere (Edgar 1995; Jacobs 2001). According to the criteria used by Phillips and Chen (2003) to distinguish Calamagrostis and Deyeuxia, most North American species of Calamagrostis fit within Deyeuxia. There has been insufficient time to evaluate the merits of their recommendation, adoption of which would require many new combinations.

Twenty-five species of Calamagrostis grow in the Flora region; one, C. epigejos, is introduced. Some species of Calamagrostis are rangeland forage grasses, but most occur too sparsely to be important for livestock. Agriculture Canada in Alberta experimented with cultivation of some western species during the 1960s and 1970s.

This treatment includes one cultivar, Calamagrostis ×acutiflora 'Karl Foerster', that is becoming increasingly popular in horticulture. A cultivar of C. canadensis has been registered for use in revegetation in arctic Alaska.

Interspecific hybridization is common; vivipary and agamospermy also occur in some species. Interspecific hybridization, polyploidy, and apomixis contribute to the taxonomic difficulty of the genus.

Some species of Calamagrostis are of interest because of their restricted distributions. These include: C. howellii (Columbia Gorge in Washington and Oregon); C. tweedyi (Washington, Oregon, and Montana); C. tacomensis (Washington and Oregon); C. ophitidis, C. foliosa, C. muiriana, and C. bolanderi (California); C. breweri (California and Oregon); and C. cainii (North Carolina and Tennessee). An incomplete draft treatment of this genus was prepared by Craig W. Greene in 1993, with minor revisions made until 1999. After Greene's death in 2003, completion of the treatment was taken up by Marr and Hebda. The taxa recognized here essentially follow Greene's concepts, with the following exceptions: Calamagrostis breweri sensu Greene (1993) has been split into C. muiriana and C. breweri sensu Wilson and Gray (2002); C. tacomensis is recognized as a species distinct from C. sesquiflora; and C. purpurascens var. laricina Louis-Marie and C. striata subsp. borealis (C. Laest.) Á. Löve & D. Love are not recognized. Descriptions of eastern North American taxa are largely based on Greene's (1980) observations. Northwestern North American taxa are described on the basis of Marr and Hebda's data and field experience. Other western United States taxa were also examined as herbarium specimens; their descriptions include observations by Marr and Hebda. Greene's key was rewritten to conform with the new data.

There is a high degree of misidentification of taxa within this genus (30% for some species in some herbaria), and species distributions should be taken as a guide only. Much more field collecting is needed for several of the taxa in order to verify their distributions, especially near the limits of their ranges. Calamagrostis is sometimes confused with Agrostis; there is no single character that distinguishes all species of Calamagrostis from those of Agrostis. In general, Calamagrostis has larger plants with larger, more substantial lemmas and paleas than Agrostis, and tends to occupy wetter habitats.

Measurements of the rachilla and callus hairs reflect the longest hairs present. Panicle widths refer to pressed specimens.The following key will enable typical specimens to be identified readily, but atypical specimens are common. For this reason, most leads require observation of a combination of characters, notably awn length, length of callus hairs relative to the lemma, glume length and scabrosity, panicle size, and leaf width.

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