A biosystematic study of the Schizachyrium scoparium complex

Abstract

Population samples of Schizachyrium scoparium, collected from Texas (vars. divergens, frequens, littorals, and virile) and New Mexico (var. neomexicanum), and herbarium specimens (including type specimens of Andropogon scoparius and vars. frequens, polycladus, villosissimus, and virilis, A. littoralis, A. neomexicanus, and S. stoloniferum) from various herbaria formed the basis for this study. Phenetic analysis showed showed that the infraspecific taxa grouped into three clusters: 1) vars. divergens and virile; 2) vars. frequens and neomexicanum; and 3) var. littorale. Variation was found to be high at intervarietal and intrapopulational levels, but less at interpopulational level. Macromorphological study demonstrated that leaf pubescence and inflorescence characteristics are genetically fixed. Photoperiodic response appears to be not under strict genetic control. Leaf color and rhizome development are habitat-influenced. In leaf anatomy, vascular bundles were assigned to four orders. Midrib anatomy was the major source of variation. Stomata were abundant on the abaxial surface, but were confined to margins on the adaxial surface (except in var. neomexicanum). Interstomatal cells were papillate in var. neomexicanum, but smooth in the other four varieties. Long cells in var. neomexicanum were shorter than those in other four varieties. Long macrohairs with basal cushion cells were frequently seen in var. divergens. Underground stem anatomy confirmed the existence of a rhizome in var. littorale. A study of type specimens suggested that var. frequens must be treated as a synonym of var. scoparium; likewise, S. stoloniferum as a synonym of var. littorale. The var. virile could not be consistently distinguished from var. divergens based on leaf pubescence, but lacked cushion cells and lemma margin trichomes; hence var. virile is treated as a forma of var. divergens. The var. neomexicanum and var. littorale, based on clear morphological differences from var. scoparium, are treated as distinct taxa. Except the var. scoparium, the other three varieties in this complex occupy definite geographical areas. Because of this distribution pattern, the four varieties are elevated to subspecies rank, ssp. scoparium, ssp. divergens, ssp. littorale and ssp. neomexicanum. This elevation and reduction necessiate four new combinations, ssp. divergens (Hack.) Gandhi, ssp. littorale (Nash) Gandhi, ssp. neomexicanum (Nash) Gandhi, and f. virile (Shinners) Gandhi.