Charlotte G. Reeder

Notes on Mexican grasses III Buchlomimus, another dioecious genus

The type of Bouteloua nervata Swallen (A. S. Hitchcock 6734) was collected in 1910 near Pachuca, Hidalgo, at an elevation of 8000 feet. No other specimens are cited along with the original description (Swallen 1939), although C. G. Pringle had collected this species in the same state in 1904. The Pringle material (No. 13241), from dry mesas near Metepec Station at 8300 feet elevation, was originally identified as Bouteloua stolonifera Scribn., and distributed with printed labels bearing that name. The type of B. stolonifera (Pringle 3174), is a quite different species, however, and is known only from the states of Zacatecas and San Luis Potosl. Moreover, the senior authors have recently shown that it is dioecious, and it has been described as a distinct genus, Cyclostachya (Reeder & Reeder 1963). In connection with the study which resulted in the description of Cyclostachya, we also examined specimens of Pringle 13241 and Hitchcock 6734. Plants of these two collections are certainly conspecific and, in fact, are quite similar except that the latter are more mature. Careful study of the spikelets revealed that although pistils with large feathery stigmas were present in many of the florets, stamens were always abortive or altogether lacking. This evidence suggested strongly that Bouteloua nervata is dioecious, and that the material before us represented only the pistillate plants. Subsequent examination of additional specimens of Pringle 13241 from other herbaria only strengthened our convictions. All plants examined had florets with well-developed pistils, but stamens, when present at all, were always abortive. The type collection, Hitchcock 6734, is apparently represented by a single sheet in the United States National Herbarium. Since we could only guess at the appearance of the staminate plants, if they indeed did exist, it seemed advisable to withhold any announcement that we suspected the species to be dioecious until we had an opportunity to search for the staminate plants in the field. In this connection, a problem arose as to the time of year at which one might reasonably expect to find the species in flower; the label on the Hitchcock sheet indicated that the plants were collected in September, whereas Pringle had gathered his material in June! In September, 1963, in connection with attendance at the II Congreso Mexicano de Bot~nica, we were able to visit the mountains near Pachuca. As we approached the type locality of Bouteloua nervata, we were filled with apprehension. There were only two collections of this species, both of them made more than half a century ago. Perhaps the species had been very rare and was now extinct. Even if it did exist, what were the chances that we could find it in flower and thus be able to determine whether or not it was really dioecious? Driving across the mesa near Ixmiquilpan, we were discouraged to note the obvious dryness of the terrain. Except for some small plants of Muhlenbergia depauperata Scribn. growing in depressions, there seemed to be few grasses in proper condition to collect. As we began the ascent in the mountains east of Pachuca, through the extensive maguey fields, there