Thinopyrum intermedium |
Poaceae tribe Triticeae |
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intermediate wheatgrass |
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Habit | Plants rhizomatous, often glaucous. | Plants annual or perennial; sometimes cespitose, sometimes rhizomatous. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Culms | 50-115 cm, glabrous or hairy, sometimes hairy only on the nodes; lowest internode plus sheath 3-5 mm thick. |
annual, not woody, usually erect, not branching above the base; internodes hollow or solid. |
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Sheaths | mostly glabrous, often ciliate on the margins; auricles 0.5-1.8 mm; ligules 0.1-0.8 mm; blades 2-8 mm wide, flat, abaxial surfaces glabrous, adaxial surfaces usually sparsely strigose, sometimes with hairs of mixed lengths, with 7-30 ribs, ribs not prominent, margins whitish, thicker than the veins. |
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. |
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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. |
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Spikes | 8-21 cm, erect or lax; internodes 7-12 mm; rachises glabrous or with hairs, scabrous on the edges, particularly distally, not disarticulating at maturity. |
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Spikelets | 11-18 mm, with 3-10 florets; disarticulation beneath the florets. |
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. |
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Glumes | oblong, glabrous and mostly smooth, or strigose with 1-1.5 mm hairs, hairs usually evenly distributed, weakly keeled distally, keels scabrous, at least distally, midvein usually more prominent and longer than the lateral veins, margins not hyaline or hyaline near the apices, apices obliquely truncate or obtuse to acute, sometimes mucronate; lower glumes 4.5-7.5 mm long, 1.5-2.5 mm wide, 5-6-veined; upper glumes 5.5-8.5 mm long, 2-3 mm wide, 5-7-veined; lemmas 7.5-10 mm, glabrous or with 1-1.5 mm hairs, hairs usually evenly distributed, sometimes only on the outer portion of the lemmas, apices occasionally awned, awns to 5 mm; paleas 7-9.5 mm, keels usually scabrous for 1/2 their length; anthers 5-7 mm. |
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. |
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Caryopses | ovoid to fusiform, longitudinally grooved, not beaked, pericarp thin; hila linear; embryos about 1/3 as long as the caryopses. |
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x | = 7. |
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2n | = 42, 43. |
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Thinopyrum intermedium |
Poaceae tribe Triticeae |
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Distribution |
AZ; CA; CO; GA; IA; ID; MA; MT; ND; NE; NJ; NM; NV; NY; OR; SD; TX; UT; WA; WY; BC; SK; YT
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Discussion | Thinopyrum intermedium is native to Europe and western Asia. It is widely established in western North America, having been introduced for erosion control, revegetation, forage, and hay. It also occurs in scattered locations further east. One of its advantages for erosion control and revegetation is that it establishes rapidly in many different habitats. In its native range, it grows in dry areas with sandy or stony soils. In Europe, it forms sterile hybrids with Elymus repens; no such hybrids are known from North America. Several subspecies have been recognized within Thinopyrum intermedium, usually based on differences in the vestiture of the glumes and lemmas, the presence or absence of lemma awns, and the color of the plants. Assadi (1994) commented that there was little correlation between the different character states. He grew seeds from several wild plants and, even when most of the offspring resembled the parent plant, there was often segregation of some variants. Crossing experiments showed that hybrids between the morphological variants were fertile, and usually had regular meiosis. He noted, however, that the plants with glabrous spikelets tended to grow in mesophytic habitats, those with hairy glumes and lemmas on dry slopes, and those with ciliate glumes and lemmas at the edges of fields and in wet places. This difference in habitat preference was reiterated by Ogle (2001). Because of this ecological distinction, they are formally recognized here as subspecies. Plants with hairs only near the lemma margins are included under T. intemedium subsp. intermedium. They may be derived from crosses between the hairy and glabrous plants, a possibility that has not been experimentally evaluated. There seems to be little correlation between spikelet vestiture and that of the leaves and stems. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 374. | FNA vol. 24, p. 238. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Triticeae > Thinopyrum | Poaceae > subfam. Pooideae | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Synonyms | Elytrigia intermedia, Elymus hispidus, Agropyron tricophorum, Agropyron intermedium var. trichophorum, Agropyron intermedium | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Name authority | (Host) Barkworth & D.R. Dewey | Dumort. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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