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Seven U. S. species of Echinochloa are recognized, five indigenous (E. polystachya, E. muricata, E. paludigena, E. walteri, E. crus-pavonis) and two adventive or introduced (E. crusgalli and E. colonum). The indigenous species are all tetraploid (2n9= 36), whereas E. crusgalli and E. colonum appear to be represented in the United States only by hexaploid (2n54) plants. A possible exception is E. crusgalli var. oryzicola for which USA counts have not been obtained, but the two published records are of tetraploid plants. Widespread and frequent throughout much of the USA are E. crusgalli and E. muricata, two species that were treated as a single species (E. crusgalli) by Hitchcock but which are distinguished by reliable morphological characters. INTRODUCTION Echinochloa is present throughout the tropical and temperate regions: of the world. Hitchcock (1936) placed the number of species at 15; Swallen (1955), Yabuno, (1962) and Gould (1968a) estimated approximately 20, and Shaw (1966) indicated 30. However, in 1966, Yabuno revised hig species estimate to 13. Morphological, cytological, embryological and anatomical features of Echinochloa are similar to those of Panicum, and this explains why the species included in Echinochloa were first placed in Panicum. Strikingly different monographic treatments of the North American species of Echinochloa were published by Hitchcock (1920) and Wiegand (1921). Hitchcock recognized seven North American species, four native, two introduced, and one, E. crusgalli, with both native and introduced or adventive varieties. Wiegand recognized 12 species, nine native and three introduced. He also listed seven varieties for the native species in addition to the typical varieties. 'Species delimitations in our treatment are in general agreement with those of 'Chase in Hitchcock's Manual (1951) except for the reclassification of a large proportion of the plants referred by her to Echinochloa crusgalli. Echinochloa crusgalli and E. muricata have been the most controversial species in the genus. Some authors have contended that crusgalli and muricata constitute one species while others have proposed five distinct species. As concluded by Fernald (1915), Wiegand (1921), Fairbrothers (1952), Ali (1968) and others, both native and adventive populations comprise the North American "barnyard grass" complex included by Hitchcock (1920, 1935) and Chase in Hitchcock's Manual (1951) in the species E. crusgalli. As delimited in the present treatment, the native plants are referrable to E. muricata (Beauv.) Fernald var. muricata, E. muricata var. microstachya Wiegand, and E. crus-pavonis var. macera. All native plants are tetraploid (2n= 36), and these commonly grow i Technical Bulletin No. T.A. 8804, Texas Agricultural Experiment Station, College Station 77843. |
