13.09 AGROPYRON Gaertn.
Mary E. Barkworth
Plants perennial; densely to loosely cespitose, sometimes rhizomatous. Culms 25–110 cm, geniculate or erect. Sheaths open; auricles usually present; ligules membranous, often erose. Inflorescences spikes, usually pectinate; middle internodes 0.2–3(5.5) mm, basal internodes often somewhat longer. Spikelets solitary, usually more than 3 times as long as the internodes, usually divergent or spreading from the rachis, with 3–16 florets; disarticulation above the glumes and beneath the florets. Glumes shorter than the adjacent lemmas, lance-ovate to lanceolate, 1–5-veined, asymmetrically keeled, a secondary keel sometimes present on the wider side, keels glabrous or with hairs, hairs not tufted, apices acute and entire, sometimes awned, awns to 6 mm; lemmas 5–7-veined, asymmetrically keeled, acute to awned, awns to 4.5 mm; paleas from slightly shorter than to exceeding the lemma, bifid; anthers 3, 3–5 mm, yellow. Caryopses usually falling with the lemmas and paleas attached. x = 7. Haplome P. Name from the Greek agrios, ‘wild’, and pyros, ‘wheat’.
Agropyron, it is now agreed, should be restricted to perennial species of Triticeae with keeled glumes, i.e., Agropyron cristatum and its allies, or the “crested wheatgrasses”. The excluded species are distributed among Pseudoroegneria, Thinopyrum, Elymus, Eremopyrum, and Pascopyrum. This leaves Agropyron as a Eurasian genus that includes diploid, tetraploid, and hexaploid plants, all of which contain a single genome, designated the P genome by the International Triticeae Consortium. The genus is now widespread in western North America, frequently being used for soil stabilization on degraded rangeland and abandoned cropland, because it is highly tolerant of grazing and provides good spring forage.
Prior to the 1930s, most Soviet agrostologists recognized two species in the genus: A. cristatum, with broad spikes; and A. desertorum (Fischer ex Link) Schult., with narrow spikes. Kosarev (1949) recognized four species, the two additional species being A. pectiniforme Roem. & Schult. and A. sibiricum (Willd.) P. Beauv.. Tsvelev (1976) recognized 10 species, within one of which, A. cristatum, he recognized nine subspecies. He considered the widely distributed taxon introduced to many different countries to be A. cristatum subsp. pectinatumi (M.-Bieb.) Tzvelev. Chen and Zhu (2006) suggested that there are 15 species in the world, five of which are present in China.
Estimating the number of species present in the Flora region is difficult, because many seed samples were brought into the region, planted out in experimental plots, and subsequently developed for various agricultural uses. In reviewing the history of crested wheatgrass in North America, Dillman (1960) stated that, based on the identifications provided with some of the early seed accessions, two species of crested wheatgrass had been introduced into North America, Agropyron cristatum and A. desertorum. He described them as “quite distinct, both in seed and plant characters” (p. 248). According to Dewey (1986), a third species, now known as A. fragilei, was introduced at about the same time; it apparently escaped Dillman’s attention.
The problem is that “taxa introduced into North America soon lose their taxonomic identity and genetic integrity because of extensive intercrossing that occurs in nursery situations” (Dewey 1986, p. 34). Despite his observations, Dewey recognized three species of Agropyron in North America, and admitted that identifying individual plants “will often be difficult and unsatisfying. Variation is continuous between the morphological extremes of the unawned, linear-spiked A. fragile to the broad, pectinate-spiked A. cristatum” (p. 38).
This treatment recognizes two species within the Flora region, a very broadly interpreted Agropyron cristatum, which includes Dewey’s A. cristatum and A. desertorum, and a traditionally interpreted A. fragile. Agropyron cristatum in North America reflects a process that might be called de-speciation.
Selected references Asay, K.H. and D.R. Dewey. 1979. Bridging ploidy differences in crested wheatgrass with hexaploid × diploid hybrids. Crop Science 19:519–523; Asay, K.H., K.B. Jensen, C. Hsiao, and D.R. Dewey. 1992. Probable origin of standard crested wheatgrass, Agropyron desertorum (Fisch. ex Link) Schultes. Canad. J. Pl. Sci. 72:763–772; Chen, S.-L. and G.-H. Zhu. 2006. Agropyron. Pp. 439–441 in Z.-Y. Wu, P.H. Raven, and D.-Y. Hong (eds.). Flora of China, vol. 22 (Poaceae). Science Press, Beijing, Peoples Republic of China and Missouri Botanical Garden Press, St. Louis, Missouri, U.S.A. 653 pp. http://flora.huh.harvard.edu/china/mss/volume22/index.htm; Dewey, D.R. 1986. Taxonomy of the crested wheatgrasses (Agropyron). Pp. 31–42 in K.L. Johnson (ed.). Crested Wheatgrass: Its Values, Problems and Myths; Symposium Proceedings. Utah State University, Logan, Utah, U.S.A. 348 pp.; Dillman, A.C. 1946. The beginnings of crested wheatgrass in North America. J. Amer. Soc. Agron. 38:237–250; Kosarev, M.G. 1949. The variability of characters of crested wheatgrass. Selekts. & Semenov. 4:41–43; Lesica, P. and T.H. DeLuca. 1996. Long-term harmful effects of crested wheatgrass on Great Plains grassland ecosystems. J. Soil Water Conservation 51:408–409; Tsvelev, N.N. 1976. Zlaki SSSR. Nauka, Leningrad [St. Petersburg], Russia. 788 pp.
1. Lemmas usually awned, awns 1–6 mm long; spikelets diverging from the rachises at angles of 30–95º; spikes narrowly to broadly lanceolate, rectangular, or ovate in outline.............................. 1. A. cristatum
1. Lemmas unawned, sometimes mucronate; spikelets diverging at an angle of less than 30(35)º; spikes linear to narrowly lanceolate in outline........................................................................................ 2. A. fragile
1. Agropyron cristatum (L.) Gaertn.
Crested Wheatgrass, Agropyron Accrêté, Agropyron à Crête
Plants occasionally rhizomatous. Culms 25–110 cm, sometimes geniculate. Ligules to 1.5 mm; blades 1.5–6 mm wide, glabrous or pubescent. Spikes 1.3–10.5(15) cm long, 5–25 mm wide, narrowly to broadly lanceolate, rectangular, or ovate, sometimes tapering distally; internodes (0.2)0.7–5(8) mm, glabrous or pilose, sometimes all more or less equal, sometimes short and long internodes alternating within a spike, basal internodes often longer than those at midlength. Spikelets 7–16 mm, diverging at angles of 30–95° at maturity, with 3–6(8) florets. Glumes 3–6 mm, glabrous or with coarse hairs on the keels, acute, usually awned, awns 1.5–3 mm; lemmas 5–9 mm, glabrous or with hairs, keeled, keels sometimes scabrous distally, apices acute, usually awned, awns 1–6 mm; anthers 3–5 mm. 2n = 14, 28, 42.
Agropyron cristatum is native from central Europe and the eastern Mediterranean to Mongolia and China. According to Tsvelev (1976), the most widely distributed taxon outside the Soviet Union is A. cristatum subsp. pectinatum. Within the Flora region, the reticulate genetic history of crested wheatgrass, and the absence of any native populations, argue against attempting recognition of subspecies.
Among the more commonly encountered variants of Agropyron cristatum in the Flora region are the cultivar ‘Fairway’, which was considered by Dillman (1946) and Dewey (1986) to belong to A. cristatum rather than A. desertorum, and its derivatives ‘Parkway’ and ‘Ruff’. The name “Fairway” is also widely used in agricultural circles to refer to any crested wheatgrass that looks like the cultivar ‘Fairway’. “Standard” crested wheatgrass, which Dewey (1986) and others placed in A. desertorum, originally referred to a particular seed lot (S.P.I. 19537) that the Montana Wheatgrowers’ Association decided to use as a standard against which to compare the performance of other crested wheatgrass strains. The term is now applied by agronomists to all crested wheatgrasses that are less leafy and have more lanceolate spikes than “Fairway” crested wheatgrasses. There are numerous cultivars of crested wheatgrass available.
Because it is easy to establish, Agropyron cristatum has often been used to restore productivity to areas that have been overgrazed, burned, or otherwise disturbed. This ability, combined with its high seed production, tends to prevent establishment of most other species, both native and introduced.
2. Agropyron fragile (Roth) P. Candargy
Plants not rhizomatous. Culms 30–100 cm, rarely geniculate. Ligules to 1 mm; blades 1.5–6 mm wide. Spikes (5)8–15 cm long, 5–13 mm wide, linear to narrowly lanceolate; internodes 1.5–5 mm. Spikelets 7–16 mm, appressed or diverging up to 30(35)º from the rachises. Glumes 3–5 mm, glabrous or hairy, often awned, awns 1–3 mm; lemmas 5–9 mm, keels scabrous distally, apices unawned, sometimes mucronate, mucros up to 0.5 mm; anthers 4–5 mm. 2n = (14), 28, (42).
Agropyron fragile is native from the southern Volga basin through the Caucasus to Turkmenistan and Mongolia. It is more drought-tolerant than A. cristatum. Within the Flora region, A. fragile appears to be uncommon outside of experimental plantings. This may change as more cultivars become available.