The Generic Subdivision of Onagraceae, Tribe Onagreae

Abstract

The Onagraceae are a small, sharply defined, homogeneous family of approximately 640 species. The family is cosmopolitan, but most diverse in the western United States and Mexico, where all knownl genera occur. Recent morphological and cytological studies have indicated some modifications of the arrangement of the family presented in 1962 (Kurabayashi, Lewis, and Raven, Amer. Jour. Bot. 49: 1003-1026). The following arrangement appears to express relationships within Onagraceae best: Tribe I. Fuchsieae. Fuchsia. Tribe II. Lopezieae. Diplandra, Lopezia, Pseudolopezia, Riesenbachia, Semtandra. Tribe III. Cireaeeae. Circaea. Tribe IV. Onagreae. Burragea, Calylophlus (see below), Camissonia (see below), Clarkia, Gaura, Gayophytum, Gongytocarpus, Hantya, Heterogaura, Oenothera (see below), Stenosiphon, Xylonagra. Tribe V. Jussiaeeae. Ludwigia. Tribe VI. Epilobieae. Boisduvalia, Epilobiuum, Zauschneria. Morphological, anatomical, and cytological studies of Onagraceae have now progressed to the point where the assignment of genera to tribes is unlikely to be affected by future discoveries or ilnvestigations of additional characters. In my opinion, there is a more evident overall phenetic relationship between Puchsieae, Lopezieae, and Cireaeeae than between these three tribes and the others; and within this group, Lopezieae and Cireaeeae seem to be especially closely related, although distinct. Jussiaeeae and Epilobieae are more similar to one another than either is to any other group. In short, the most distinctive assemblage of genera in the family is Onagreae. Onagreae are an exclusively American group, although several species have been introduced into the Old World, and some are widespread there. At the time of Linnaeus, representatives of only two genera-Oenothera and Gaurawere known. To these the others were added gradually, beginning with the botanical exploration of western North and South America and Mexico from the end of the 18th Century onward. The first comprehensive 'attempt to subdivide the group generically was that of fdouard Spach, first in the Histoire Naturelle des Vegetaux (4: 335-416. 1835), and later the sanme year in his "Monographia Onagrearum" (Nouv. Ann. Mus. Paris III. 4: 321-408, pl. 30-31. 1835). Spach visualized geniera as sharply defined, homogeneous assemblages containing few species, and as a result proposed numerous new genera of Onagraceae. On the other hand, American botanists concerned with the group tended to recognize very few, large genera. For example, in their Flora of North America (1840), Torrey and Gray treated most of Spach's proposed genera as sections or subgenera, and included elements of Clarkia anid even Boisditvatia in Oenothera. Yet they maintained as distinet Eulobuts, now generally included in Oenothera, and Eutcharidium, now included in Clarkia. Later Sereno Watson, in his "Revision of the extra-tropical North American species of the genus Oenothera" (Proc. Amer. Acad. 8: 573-618. 1873) kept