SYSTEMATICS OF SOUTH AMERICAN TRIPSACUM (GRAMINEAE)

The genus Tripsacum is widely distributed between 42?N and 240S latitude. In South America, the genus extends around the Amazon and Orinoco basin, and from the Caribbean coast south to Brazil and Paraguay. The most common South American taxon is T. dactyloides (L.) L. var. meridonale de Wet and Timothy (2n = 36), which differs from North American representatives of the species in having subdigitate recemes usually appressed with the apical male sections typically curved. Closely related to T. dactyloides, but usually occupying more seasonally moist and dry habitats, is T. australe Cutler and Anderson. This species is typically robust with the basal leaf sheaths tomentose, and the much elongated culms becoming decumbent in older plants. Smaller plants, with essentially erect culms and leaf sheaths on the culms hirsute rather than tomentose, are recognized as T. australe var. hirsutum de Wet and Timothy. The two varieties of T. australe are both diploid (2n = 36) and they cross to produce fertile hybrids. They also cross with T. dactyloides var. meridonale (2n = 36), but these hybrids are partially sterile. Tripsacum cundinamarce de Wet and Timothy (2n = 36) is a robust species with glaucus leaves. It resembles robust specimens of T. dactyloides in having glabrous leaf sheaths, but can always be recognized by inflorescences that are composed of racemes arranged along a several-noded primary axis. This species is confined to moist habitats, while T. dactyloides occupies a range of habitats in South America. Tripsacum peruvianum de Wet and Timothy is a gametophytic apomict with 2n = 72, 90 or 108 chromosomes. It is characterized by an erect growth habit and strongly hirsute leaf sheaths. The cultivated Guatemala grass, T. andersonii Gray, occurs spontaneously in the mountains of Venezuela, Colombia, and Peru. This sexually sterile species is characterized by 2n = 64, and may combine 54 Tripsacum and 10 Zea chromosomes in its genome. Electrophoretic patterns of seed storage proteins confirm the validity of recognizing T. cundinamarce as distinct from T. dactyloides, and T. peruvianum as distinct from T. australe. THE GENUS Tripsacum (Gramineae) is monoecious, New World in distribution and related to Zea. Biosystematic interest in Tripsacum was initiated when Mangelsdorf and Reeves (1939) proposed that introgression with Zea mays L. may have contributed to racial evolution of domesticated maize. The genus was reviewed by Cutler and Anderson (1941) who recognized seven species, T. australe Cutler and Anderson in South America, and T. foridanum Porter ex Vasey, T. dactyloides (L.) L., T. lanceolatum Rupr. ex Fourn., T. fasciculatum Trin. ex Ascherson, T. pilosum I Received for publication 4 February 1980; revision accepted 24 May 1980. The authors wish to thank L. F. Randolph who was instrumental in making arrangements for land to establish a Tripsacum nursery and for his collaboration in observations on the material, Fairchild Tropical Garden for use of the land, and Pioneer Hi-Bred, International, for nursery maintenance. This has been a cooperative investigation of the Illinois Agricultural Experiment Station and the North Carolina Agricultural Research Service. This research was supported in part by NSF Grant DEB 78-00538 to D. H. Timothy, North Carolina, and CSRS Grant 61615-60 to J. M. J. de Wet. Scrib. and Merrill and T. latifolium Hitchc. in North and Central America. Two Meso-American species, T. maizar Hern. and Randolph, and T. zopilotense Hern. and Randolph were added to the genus by Hernandez and Randolph (1950), and de Wet, Gray and Harlan (1976) further recognized T. andersonii Gray a widely cultivated taxon, and T. bravum Gray a species from Mexico. It was further indicated by de Wet, Gray and Harlan (1976) that T. dactyloides extends across the range of the genus from about 420 north to 240 south lati-