Axillary Cleistogenes in Stipa Leucotricha and their Role in Nature

Abstract

Texas needlegrass (Stipa leucotricha Trin. and Rupr.) is the principal and usually the only stipa on the prairies of the eastern half of Texas. In this area it is widely recognized and appreciated by ranchers because of its winter-growth habit. Locally it is commonly known as winter speargrass, or, curiously enough, as stipa. Its most common associate in pastures is buffalo grass (Buchloe dactyloides (Nutt.) Engelm.). On some severely overgrazed pastures, particularly those with deep, heavy, clay soils, stipa is the principal perennial grass. During 1943 and 1944 stipa was studied intensively on the Fort Worth Prairie, west of the city of Fort Worth, Texas. Here it is abundant in overgrazed pastures, though ordinarily absent on lands subjected to no greater disturbance than removal of an annual crop of native hay. Its ability to withstand intensive grazing use and the fact that it is the only native perennial grass providing considerable green pasturage during winter, cause itto be of especial interest. This interest is heightened because it is the only stipa in continental United States reported by Hitchcock ('35) to have cleistogenes. Concerning Stipa leucotricha, he stated Cleistogamous spikelets with glumes obsolete and lemma nearly awnless are borne in basal sheaths just after maturity of panicle. The r6le of these plump, commonly subterranean, grains is apparently little known. The morphology of axillary cleistogenes in several American grasses has been treated by Chase ('18) whose article also prompted this study into autecological aspects because of the statement I surmise that the grains germinate within the sheath and push root and shoot through the internerves but this has not been proved by experiment. PURPOSE AND METHODS OF STUDY