Kendrick L. Marr Richard, J. Hebda and Craig W. Greene†

Plants perennial; often cespitose, usually rhizomatous. Culms 10–210 cm, unbranched or branched, more or less smooth, nodes 1–8. Sheaths open, smooth or scabrous; auricles absent; ligules membranous, usually truncate to obtuse, sometimes acute, entire or lacerate, lacerations often obscuring the shapes; blades flat to involute, smooth or scabrous, rarely with hairs. Inflorescences panicles, open or contracted, sometimes spikelike; branches appressed to more or less drooping, some branches longer than 1 cm. Spikelets pedicellate, weakly laterally compressed, with 1(2) florets; rachillas prolonged beyond the base of the distal floret(s), usually hairy; disarticulation above the glumes. Glumes membranous, subequal, equal to, or longer than the lemmas, rounded or keeled, backs smooth or scabrous, rarely long-scabrous with bent projections, veins obscure to prominent, apices acute to acuminate, rarely awn-tipped or attenuate; lower glumes 1(3)-veined; upper glumes 3-veined; calluses hairy, hairs 0.2–6.5 mm, sparse to abundant; lemmas 3(5)-veined, smooth or scabrous, apices usually tapering into 4 teeth, awned; awns arising from near the base to near the apices,straight or bent, sometimes delicate and indistinct from the callus hairs, sometimes exserted beyond the lemma margins; paleas well developed, almost as long as to slightly longer than the lemmas, thin, 2-veined; anthers 3, sometimes sterile. Caryopses shorter than the lemmas, concealed at maturity, oblong, usually glabrous. x = 7. Name from the Greek calamos, ‘reed’, and agrostis, ‘grass’.

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. The merits and implications of their recommendation, adoption of which would require many new combinations, have not yet evaluated.

Twenty-five species of Calamagrostis grow in North America north of Mexico. 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 in North America. 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. strictasubsp. borealis (C. Laest.) Á. Löve & D. Löve 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 Calamagrostisfrom 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 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.

SELECTED REFERENCES Edgar, E. 1995. New Zealand species of Deyeuxia P. Beauv. and Lachnagrostis Trin. (Gramineae: Aveneae). New Zealand J. Bot. 33:1–33; Greene, C.W. 1980. The systematics of Calamagrostis (Gramineae) in eastern North America. Ph.D. dissertation. Department of Biology, Harvard University, Cambridge, Massachusetts, U.S.A. 238 pp.; Greene, C.W. 1984. Sexual and apomictic reproduction in Calamagrostis (Gramineae) from eastern North America. Amer. J. Bot. 71:285–293; Greene, C.W. 1993. Calamagrostis, Reed Grass. Pp. 1243–1246 in J.C. Hickman, ed. The Jepson Manual: Higher Plants of California. University of California Press, Berkeley, California, U.S.A. 1400 pp.; Harmon, P.J. 1981. The vascular flora of the ridge top of North Fork Mountain, Grant and Pendleton counties, West Virginia. Master’s thesis, Southern Illinois University, Carbondale, Illinois, U.S.A. 434 pp.; Hitchcock, C.L., A. Cronquist, and M. Ownbey. 1969. Vascular Plants of the Pacific Northwest. Part 1: Vascular Cryptogams, Gymnosperms, and Monocotyledons. University of Washington Press, Seattle, Washington, U.S.A. 914 pp.; Hultén, E. 1968. Flora of Alaska and Neighboring Territories. Stanford University Press, Stanford, California, U.S.A. 1008 pp.; Jacobs, S.W.L. 2001. The genus Lachnagrostis (Gramineae) in Australia. Telopea 9:439–448; Kawano, S. 1965. Calamagrostis purpurascens R. Br. and its identity. Acta Phytotax. Geobot. 21:73–90; Marr, K.L. and R.J. Hebda. 2006. Calamagrostis tacomensis (Poaceae), a new species from Washington and Oregon. Madroño 53:290–300; Phillips, S.M. and W.-L. Chen. 2003. Notes on grasses (Poaceae) for the Flora of China, I: Deyeuxia. Novon 13:318–321. Reznicek, A.A. and E.J. Judziewicz. 1996. A new hybrid species, ×Calammophila don-hensonii (Ammophila breviligulata × Calamagrostis canadensis, Poaceae) from Grand Island, Michigan. Michigan Bot. 35:35–40; Wilson, B.L. and S. Gray. 2002. Resurrection of a century-old species distinction in Calamagrostis. Madroño 49:169–177.

Key to species in North America north of Mexico.

©Utah State University; reproduced with permission.