THE THREE SPECIES OF STILLINGIA (EUPHORBIACEAE) IN FAR WESTERN TEXAS

Keys, descriptions, and notes on nomenclature, ecology, and dis- tribution are given for Stillingia Treculiana, S. sylvatica, and S. texana of the trans-Pecos and adjacent counties. No new names or taxa are published. For our three species of Stillingia complete and accurate descriptions and notes on ecology and detailed distribution in extreme western Texas are given for the first time in this, another of our papers on the members of this family in this poorly known region. An index map of the region was published previously (Johnston and Warnock, 1962). From among our other euphorbiads the members of this genus can be picked out on the basis of their herbaceous habit, and terminal spikelike inflorescences which are, more precisely, spiciform thyrses, and the glandlike stipules at the bases of the bracts as large as the bracts themselves. They are unusual also in their lack of pubescence, and in that each of the 3 styles is entire, and in the milky sap. A distinctive characteristic, and the one which distinguishes Stillingia from the very closely related tropical genus Sapium, as well as from our other genera, is the enlargement and induration of the lower portion of the ovary, its separation at maturity from the upper dehiscent por- tion, and its persistence as a triangular or three-pointed gynobase. The columella, a common postdehiscence feature among our euphorbiads, in Stillingia is fragile and does not long persist. KEY