Family: Poaceae |
Laura A. Morrison Plants annual. Culms-14-180 cm, solitary or branched at the base; internodes usually hollow throughout in hexaploids, usually solid for about 1 cm below the spike in diploids and tetraploids, even if hollow below. Sheaths open; auricles present, often deciduous at maturity; ligules membranous; blades flat, glabrous or pubescent. Inflorescences usually terminal spikes, distichous, with 1 spikelet per node, occasionally branched; internodes (0.5)1.4-8 mm; disarticulation in the rachis, the spikelets usually falling with the internode below to form a wedge shaped diaspore, sometimes falling with the adjacent internode to form a barrel shaped diaspore, domesticated taxa usually non disarticulating, or disarticulating only under pressure. Spikelets 10-25(40) mm, usually 1-3 times the length of the internodes, appressed to ascending, with 2-9 florets, the distal florets often sterile. Glumes subequal, ovate, rectangular, or lanceolate, chartaceous to coriaceous, usually stiff, tightly to loosely appressed to the lower florets, with 1 prominent keel, at least distally, keels often winged and ending in a tooth or awn, a second keel or prominent lateral vein present in some taxa; lemmas keeled, chartaceous to coriaceous, 2 lowest lemmas usually awned, awns 3-23 cm, scabrous, distal lemmas unawned or awned, awns to 2 cm; paleas hyaline membranous, splitting at maturity in diploid taxa; anthers 3. Caryopses tightly (hulled wheats) or loosely (naked wheats) enclosed by the glumes and lemmas, lemmas and paleas not adherent; endosperm flinty or mealy. x = 7. Haplomes A, B, D, and G. Triticum is the classical Latin name for wheat. Triticum is a genus of approximately 25 wild and domesticated species. It was first cultivated in western Asia at least 9,000 years ago and is now the world’s most important crop, being planted more widely than any other genus. Triticum is native to western and central Asia. It includes diploids (A haplome), tetraploids (AB or AG haplomes), and hexaploids (ABD or AAG haplomes). The world’s only reserve designed to protect native populations of wild cereals, the Erebuni Reserve, is located just outside Yerevan, Armenia. It is home to three wild species ofTriticum: T. araraticum Jakubz., T. boeoticum, and T. urartu. Only Triticum aestivum, T. durum, and T. speltaare grown commercially in North America,T. aestivum being by far the most important. The remaining species in this treatment are those most frequently grown by North American plant breeders and wheat researchers. None of the species has become an established part of the North American flora, but they may be encountered as escapes near agricultural fields and research stations, or along transportation routes. Triticum is sometimes treated as including Aegilops, but the taxa in these genera differ morphologically and ecologically. In addition, species of Triticum sensu stricto are unique in possessing the A haplome, of which there are two forms, Au and Ab. Of the other three haplomes present in Triticum, the D haplome is derived from Aegilops tauschii(Dvorak et al. 1998), and theB and G haplomes are thought to be derived from an S haplome taxon of Aegilops (Giorgi et al. 2003). The treatment presented here is based on Dorofeev and Migushovas (1979) monograph of Triticum sensu stricto, with some modification. The assignment of species status to domesticated forms is controversial. It is done here for convenience, and to aid in distinguishing between taxa with distinct morphological, ecological, and evolutionary traits. For a genomically based treatment, see Kimber and Sears (1987). Spring wheat and winter wheat refer to the growing season. Spring wheat is planted in the spring and harvested in the summer of the same year; winter wheat is planted in the fall and harvested the following summer. Hard wheat and soft wheat are terms used to describe wheats with flinty or mealy endosperm, respectively. Flinty endosperm has a higher protein content and is harder than mealy endosperm. At the species level, soft wheat refers to T. aestivum; hard wheat refers to T. durum. Within T. aestivum, endosperm type also is graded as either soft or hard; it is never as hard (flinty) as in T. durum. The width of a spike is the distance from one spikelet edge to the other across the two rowed side of the spike; its thickness is the distance across the frontal face of spikelet, from one edge to the other. The spike and spikelet measurements do not include the awns. The glumes are measured from the base to the shoulder, and do not include any toothed tip. SELECTED REFERENCES Dorofeev, V.F. and E.F. Migushova. 1979. Pshenitsa [Wheat]. (Vol. 1 in V.F. Dorofeev and O.N. Korovina (eds.). Kul’turnaia Flora SSSR [Flora of Cultivated Plants of the USSR]). Kolos, Leningrad [St. Petersburg], Russia. 346 pp. [In Russian; English translation (in prep.) used]; Dvorak, J., Z. C. Luo, Z. L. Yang, and H. B. Zhang. 1998. The structure of the Aegilops tauschii genepool and the evolution of hexaploid wheat. Theor. Appl. Genet. 97:657-670;Giorgi, D., R. D’Ovidio, O.A. Tanzarella, C. Ceoloni, and E. Porceddu. 2003. Isolation and characterization of S genome specific sequences from Aegilops sect. Sitopsis species. Genome 46:478-489; Kimber, G. and E.R. Sears. 1987. Evolution in the genus Triticum and the origin of cultivated wheat. Pp. 154-164in E.G. Heyne (ed.). Wheat and Wheat Improvement, ed. 2. American Society of Agronomy, Madison, Wisconsin, U.S.A. 765 pp.; Morrison, L.A.2001. The Percival Herbarium and wheat taxonomy: Yesterday, today, and tomorrow Pp. 65-80in P.D.S. Caligari and P.E. Brandham (eds.) Wheat Taxonomy: The Legacy of John Percival. Linnean Special Issue No. 3. Academic Press, London, England. 190 pp.; Percival, J. 1921. The Wheat Plant. Duckworth, London, England. 463 pp. T.A. Cope (1995) Triticum. Flora of Somalia 4: 157. Plants annual or perennial. Ligules membranous. Inflorescences terminal, spikes bearing solitary spikelets, rachises fragile (breaking up at maturity) or not (not in cultivated species). Spikelets with 3-9 florets; glumes oblong to ovate, coriaceous, 5-11-veined, 1-2-keeled, sometimes the lower portion becoming rounded as the grain expands, tips obtuse, truncate, or 2-toothed, lateral veins diverging into the teeth; lemmas rounded on the back or keeled near the top, tips similar to those of the glumes. The number of species recognized in Triticum varies widely, from 5 to around 25 but only one, Triticum aestivum, is known from Somaliland and Somalia. It is the source of most of the wheat flour used for bread-making. The global distribution map of the genus reflects the widespread cultivation of bread wheat. Global distribution of Triticum. Note: GBIF records include introduced and cultivated plants. Consequently, the distribution shown often differs from statements about a taxon's native distribution. |