Plants annual or perennial; sometimes cespitose, sometimes rhizomatous. Culms annual, not woody, usually erect, not branching above the base; internodes hollow or solid. Sheaths usually open, those of the basal leaves sometimes closed; collars without tufts of hair on the sides; auricles usually present; ligules membranous or scarious, sometimes ciliolate, those of the upper and lower cauline leaves usually similar; pseudopetioles absent; blades linear to narrowly lanceolate, venation parallel, cross venation not evident, without arm or fusoid cells, surfaces without microhairs, not papillate, cross sections non-Kranz. Inflorescences usually spikes or spikelike racemes, with 1-5 sessile or subsessile spikelets per node, occasionally panicles, sometimes with morphologically distinct sterile and bisexual spikelets within an inflorescence; pedicels absent or to 4 mm; disarticulation usually above the glumes and beneath the florets, sometimes in the rachises, sometimes at the inflorescence bases. Spikelets usually laterally compressed, sometimes terete, with 1-16 bisexual florets, the distal (or only) floret sometimes sterile; rachillas sometimes prolonged beyond the base of the distal floret. Glumes unequal to equal, shorter than to longer than the adjacent florets, subulate, lanceolate, rectangular, ovate, or obovate, 1-5-veined, absent or vestigial in some species; florets laterally compressed to terete; calluses glabrous or hairy; lemmas lanceolate to rectangular, stiffly membranous to coriaceous, sometimes keeled, 5(7)-veined, veins not converging distally, inconspicuous, apices entire, lobed, or toothed, unawned or awned, awns terminal, unbranched, lemma-awn junction not evident; paleas usually subequal to the lemmas, sometimes considerably shorter or slightly longer than the lemmas; lodicules 2, without venation, usually ciliate; anthers 3; ovaries with hairy apices; styles 2, bases free. Caryopses ovoid to fusiform, longitudinally grooved, not beaked, pericarp thin; hila linear; embryos about 1/3 as long as the caryopses. x = 7.
Discussion
The Triticeae are primarily north-temperate in distribution. The tribe includes 400-500 species, among which are several important cereal, forage, and range species. Its generic treatment is contentious. Linnaeus (1753) recognized five genera among the species now included in the tribe; Hordeum and Secale are the only two that still have his circumscription. Hordeum is also the only genus to include both annual and perennial species. The lack of agreement concerning the generic treatment of the tribe reflects the prevalence of natural hybridization, introgression, polyploidy, and reticulate relationships among its species. These factors preclude the circumscription of monophyletic groups, and mitigate against the delineation of morphologically coherent groups. Tzvelev (1975) argued that these same factors contribute to the tribe's success by maintaining a "generalist" genome.
The major disagreement in the treatment of the annual genera concerns Triticum and Aegilops. Some (e.g., Kimber and Feldman 1987) advocate treating them as a single genus in recognition of their close genetic similarity; others argue for maintaining them as separate genera (e.g., van Slageren 1994). Love (1984) divided them among 14 genera. They are accepted here in their traditional senses, despite the strong argument for their combination, largely in deference to the wealth of literature, reports, and genetic resources that have been accumulated under these two names. Spontaneous hybridization and introgression between the two are common, and most species of Triticum are derived from hybrids between the two genera. Nevertheless, they differ in their ecology and, to some extent, in their morphology.
Treatment of the perennial species is more contentious. Restriction of Agropyron to what are known in English as the crested wheatgrasses is universally accepted; most taxonomists also accept the placement of alkaline-tolerant species that are strongly rhizomatous or have short, subulate glumes in Leymus. Pseudoroegneria, Pascopyrum, and Thinopyrum are less accepted. They are widely accepted by those working in genetic resources, but less so by those involved in floristics who prefer to include them in Elymus; all were traditionally included in Agropyron. Another area of disagreement is the treatment of Elytrigia Desv., Roegneria K. Koch, and Hystrix Moench. Species sometimes placed in Elytrigia are here included in Elymus, Thinopyrum, or Pseudoroegneria; species of Roegneria in Elymus; and species of Hystrix in Elymus or Leymus. Wide acceptance of a single treatment is hampered by the existence of differing taxonomic traditions, and by the lack of a coordinated international examination of morphological variation among the tribe's species.
The treatment followed here is strongly influenced by the treatments of Love (1984) and Dewey (1984), particularly with respect to the perennial genera. Both advocated using genomic constitution as the basis for generic delimitation in the tribe. The genomic constitution of individual species is determined by observing meiotic chromosome pairing in hybrids. The base chromosome number in the tribe is seven. If a hybrid between two tetraploids forms 7 quadrivalents and 14 bivalents at meiosis, its parents are considered to have one similar set of chromosomes or haplome, and one dissimilar haplome. The three haplomes can then be assigned codes. For example, one parent might be said to have the E and F haplomes, or an EF genomic constitution, and the other the E and L haplomes, or an EL genomic constitution. The prevalence of polyploids and the ease of forming hybrids in the Triticeae has enabled cytogeneticists to build up a rather complete picture of the genomic constitution of its members. This led to the discovery that there is a strong, but not perfect, correlation between morphology and genomic constitution. The haplome codes used in this volume are those endorsed by the International Triticeae Consortium (http://herbarium.usu.edu/Triticeae/genmsymb.htm). Molecular tools reveal a pattern that is, in general, consistent with the cytogenetic data, but they often reveal an underlying complexity that cannot be discerned using only classical cytogenetic techniques.
Selected References
Lower Taxa
Key
| 1 | Spikelets 2-7 at all or most nodes. | > 2 |
| 2 | Spikelets 3 at each node, the central spikelets sessile, the lateral spikelets usually pedicellate, sometimes all 3 spikelets sessile in cultivated plants; spikelets with 1 floret, usually only the central spikelet with a functional floret, the florets of the lateral spikelets usually sterile and reduced, in cultivated plants all florets functional or those of the lateral spikelets functional and those of the central spikelet reduced | Hordeum |
| 2 | Spikelets usually other than 3 at each node, if 3, all three sessile; spikelets with 1-11 florets, if 1 floret, additional reduced or sterile florets present distal to the functional floret in at least 1 spikelet per node. | > 3 |
| 3 | Lemmas strongly keeled, keels conspicuously scabrous distally, scabrules 0.5-0.8 mm long; lemma awns straight | Secale |
| 3 | Lemmas rounded proximally, sometimes keeled distally, keels not or inconspicuously scabrous distally; lemma awns straight, flexuous, or variously curved. | > 4 |
| 4 | Plants annual, weedy; spikelets with only 1 bisexual floret | Taeniatherum |
| 4 | Plants perennial, usually not weedy; spikelets usually with more than 1 bisexual floret. | > 5 |
| 5 | Lemma awns (0)1-120 mm long; anthers 0.9-6 mm long; blades with well-spaced, unequally prominent veins on the adaxial surfaces | Elymus |
| 5 | Lemmas usually unawned or with awns up to 7 mm long, if awns 16-35 mm long, anthers 6-8 mm; blades usually with closely spaced, equally prominent veins on the adaxial surfaces. | > 6 |
| 6 | Disarticulation in the spikelets, beneath the florets; plants sometimes cespitose, often rhizomatous | Leymus |
| 6 | Disarticulation tardy, in the rachises; plants cespitose, not rhizomatous | Psathyrostachys |
| 1 | Spikelets 1 at all or most nodes. | > 7 |
| 7 | Spikelets usually more than 3 times the length of the middle rachis internodes, usually divergent, sometimes ascending; rachis internodes 0.2-5.5 mm long. | > 8 |
| 8 | Glumes with 2 prominent keels, keels with tufts of hair | Dasypyrum |
| 8 | Glumes initially with 1 keel, sometimes 2-keeled at maturity, keels glabrous or hairy, hairs never in tufts. | > 9 |
| 9 | Plants annual; anthers 0.4-1.4 mm long; spikes 0.8-4.5 cm long | Eremopyrum |
| 9 | Plants perennial; anthers 3-5 mm long; spikes 1.3-15 cm long | Agropyron |
| 7 | Spikelets 72-3 times the length of the middle rachis internodes, appressed or ascending; rachis internodes 3-28 mm long. | > 10 |
| 10 | Glumes subulate to narrowly lanceolate, tapering from below midlength, 1(3)-veined at midlength. 11. Glumes lanceolate, tapering to acuminate apices from near midlength or below, keels curving to the side distally; plants always rhizomatous | Pascopyrum |
| 11 | Glumes subulate to lanceolate, tapering from below midlength, keels straight or almost so; plants often rhizomatous | Leymus |
| 10 | Glumes lanceolate, rectangular, ovate, or obovate, narrowing beyond midlength, often the in distal 1/4 (1)3-5(7)-veined at midlength. | > 11 |
| 12 | Plants annual; glumes often with lateral teeth or awns, midveins smooth throughout. | > 13 |
| 13 | Glumes rounded over the midveins; plants weedy | Aegilops |
| 13 | Glumes keeled over the midveins; plants cultivated, sometimes escaping | Triticum |
| 12 | Plants perennial; glumes without lateral teeth or awns, midveins sometimes scabrous. | > 14 |
| 14 | Glumes stiff, truncate, obtuse, or acute, unawned; glume keels smooth proximally, usually scabrous distally | Thinopyrum |
| 14 | Glumes flexible, acute to acuminate, sometimes awn-tipped; glume keels usually uniformly smooth or scabrous their whole length, sometimes smooth proximally and scabrous distally. | > 15 |
| 15 | Spikelets distant, not or scarcely reaching the base of the spikelet above on the same side of the rachis; anthers 4-8 mm long | Pseudoroegneria |
| 15 | Spikelets usually more closely spaced, reaching midlength of the spikelet above on the same side of the rachis; anthers 0.7-7 mm long | Elymus |