Morphogeography of Four Grass Taxa in North-Central and Eastern Texas

Abstract

Field studies in north-central and eastern Texas and examination of herbarium vouchers from that area substantiated a garden study of vegetative characteristics of transplanted clones of Andropogon scoparius Michx., Andropogon gerardi Vitman, Sorghastrum nutans (L.) Nash, and Panicum virgatum L. Plants in these taxa in the pine forests of eastern Texas were extremely pubescent and non-glaucous. Proceeding westward to central Texas, the plants were less pubes- cent and this pubescence was replaced by glaucousness in the plants of the open woodlands and grassland of central Texas. Clonal segments of the grasses grown in 3 soils in a greenhouse, under high light intensity, were not altered in the degree of pubescence and glaucousness. Under low light intensity, clonal segments were slightly altered in glaucousness, but not in pubescence. Of the North American prairie grasses represented in the vegeta- tional mosaic of Texas, Andropogon scoparius Michx., Andropogon gerardi Vitman, Sorghastrum nutans (L.) Nash., and Panicum virga- tum L. are among the most widespread. In Texas, they occur in pine forests, oak-hickory forests, coastal prairies, inland prairies, live oak- juniper forests, and montane forests. The wide range of habitats rep- resented from the Gulf Coast to the Trans-Pecos and the accompany- ing diversity of soils, climates, and biota are reflected by the vegeta- tional diversity within the state. Morphological differentiation within the 4 grasses is geographically correlated in Texas. An initial investigation of the morphogeographic patterning within transplanted clones (Bragg and McMillan, 1962) demonstrated that extremely pubescent foliage predominated in plants from eastern Texas and that glaucous foliage predominated in plants from central Texas. Within the transplanted series, patterning in- cluded diverse combinations of pubescent and glaucous plants from various geographic areas. In a comparison of the 4 grasses from 7 lo- cations, including Trans-Pecos, northwest central, south central, northeast central, eastern and south coastal Texas and the Texas Pan- handle, species-population samples from Lufkin in eastern Texas had the greatest predominance of pubescent plants and samples from Leuders in northwest central Texas had the greatest concentration of glaucous plants. To determine the incidence of pubescent and glaucous plants in