Morphogeography of Four Grass Taxa in Texas

Abstract

Morphological variation in certain vegetative characteristics were studied in Texas within four widespread grass taxa: Andropogon scoparius Michx. complex, the Andropogon gerardi Vitmanhallii Hack. complex, Sorghastrum nutans (L.) Nash., and Panicum virgatum L. Clonal material, transplanted in February, 1959, was compared during 1960 and 1961 in an experimental garden at Austin. The taxonomic status of the taxa indicated that each is highly variable and includes intergradation of geographic variants. Within the state, morphological variation is shown in each of the 4 taxa by the extremely pubescent, non-glaucous plants of eastern Texas and by the extremely glaucous, glabrous plants of northwest central Texas. The pubescent forns predominate in the pine forests of eastern Texas; the glaucous forns, in the open woodlands and grasslands of northwest central Texas. Some historical linkage in their distribution, possibly correlated with postPleistocene movements, has accounted for the high incidence of pubescent forns from Texas to Missouri, and for the predominance of glaucous plants from Texas to Nebraska. In the grassland communities of Texas, morphological differentiation within a number of grass taxa is geographically correlated. Extremely pubescent foliage predominates in eastern Texas; glaucous foliage in northwest central Texas. This study was begun to ascertain morphological patterning within four of these diverse and widespread taxa. Since pubescence and glaucescence might be altered environmentally, there was advantage -to studying the material under the single habitat of the transplant garden in Austin. This transplant material, previously studied for behavior patterning (McMillan, 1961), formed the basis of a community study in Texas. The combined morphogeographic study and behavior comparison provides clues to the mechanism of grassland distribution. MATERIALS AND METHODS Texas clones of the Andropogon scoparius Michx. complex, the Andropogon gerardi Vitman-hallii Hack. complex, Sorghastrum nutans (L.) Nash., and Panicum virgatum L. were compared for vegetative d1ifferences during the latter half of June, 1960 and 1961. These clones were moved to Austin in February, 1959. Each clone, split into two segments before planting, was well established at the time of comparison. 1 Studies were aided by funds from National Science Foundation Grant G-6166 and G-14909. 2 National Science Foundation Research Participant, 1960, 1961. Permanent address: Department of Biology, Arlington State College, Arlington, Texas.