From Plant Press Vol. 10, No. 4 from October 2007.
Warren L. Wagner, along with Missouri Botanical Garden collaborators Peter C. Hoch, and Peter H. Raven, recently published “Revised Classification of the Onagraceae” in Systematic Botany Monographs (83: 1-240; 2007). The book represents the culmination of many years work in the family, especially by Peter Raven, his students and collaborators. It is the first comprehensive classification of the family since 1893 and the first complete listing of recognized taxa since 1832. Moreover, this synopsis is the first to review and integrate significant diagnostic characters from the extensive literature on the family for all taxa above the species level, and summarizes information on chromosome numbers, breeding systems and pollinators, and geographic and ecological distributions for each species group formally recognized.
Recent molecular phylogenetic analyses in the plant family Onagraceae, carried out primarily at the Smithsonian Institution by post-doctoral fellow Rachel Levin and others, provided critical evidence that underlies this revision of the family classification. Wagner, Hoch and Raven developed this recent monograph over the past several years by bringing together the new molecular phylogeny with the broad array of morphological characters known in the family, and expressing this in the context of the nomenclatural history of Onagraceae. The new publication also provides a species level synopsis of the family, incorporating all nomenclatural changes and combinations but not full species-level synonymy. It presents descriptions of all taxa recognized for the first time, as well as tribes, genera, sections, subsections, and series.
The new classification recognizes 22 genera in the Onagraceae, subdivided into two subfamilies, Ludwigioideae (only Ludwigia) and Onagroideae (the other genera), and the latter into six tribes, two with only one genus each, three with two genera each, and one (tribe Onagreae) with 13 genera. The authors list recognized taxa for each group. Many changes involve the tribe Onagreae, from which the authors segregate Gongylocarpus as its own tribe, sister to tribes Epilobieae and Onagreae, and within which they propose changes in the delimitation of Camissonia and Oenothera. Camissonia as currently defined is broadly paraphyletic, and the new classification recognizes nine generic lineages (Camissonia, Camissoniopsis, Chylismia, Chylismiella, Eremothera, Eulobus, Holmgrenia, Taraxia, and Tetrapteron), which in part form a grade at the base of Oenothera. Each of these lineages is well-supported by morphological and molecular data. In contrast, molecular and morphological data both suggest the need to broaden the delimitation of Oenothera to include Calylophus, Gaura, and Stenosiphon. This redefined Oenothera, strongly supported by molecular data, is marked by at least two morphological synapomorphies: the presence of an indusium on the style, and a lobed or peltate stigma.
This publication represents a major advance in our understanding of the family Onagraceae, which itself represents one of the most characteristic plant families that have radiated in western North America, even though the family is cosmopolitan. This new publication provides a broad summary of the molecular, morphological, and geographical information on this important family, and should provide stimulus to additional research on a group that already is a model for plant evolutionary studies.