Generic and Sectional Delimitation in Onagraceae, Tribe Epilobieae

The available evidence is used to produce a revised taxonomy for Onagraceae tribe Epi bieae, with two genera, Epilobium 2 Boisduvalia.Zauschneria is a specialized, bird-с.taxon closely related to one oun © f Epilobium, and it is СЕЕ reduced to the status of і section of that genus.It is treated as comprising a single species with three tetraploid (n -15) and three ари (п = 30) $ ah pce: тоон hick extensive intergradation occurs.Chamerion (Chamaenerion), a Eurasian group of seven species, two reaching Nort ica, is closely related to and doubtless shares a common ancestor with Epilobium sect.E DD the other four sections are more distantly related.ey include a total of seven species, all xerophytes confined to western North America, the probable place d origin of хш tribe.и is treated as comprising two sections in place of the three recognized earlie based upon further morphological studies and evidence obtained from artificial hybridization 1e taxonomy proposed for the tribe Epilobieae appears to provide a balanced classification for the ce that brings it into line with the other five tribes and 15 genera of the family.The tribe Epilobieae, with some 210 species, differs from the other five tribes in the family Onagraceae (Raven, 1964b) in its dotlike, almost entirely heteropycnotic chromosomes that persist as chromatic dots through interphase ( Kurabayashi et al., 1962); basic chromosome numbers x -9, 10, 12, 13, 15, 16, and 18; occurrence of many species in moist places; and, in all but a few species, the habit of shedding the mature pollen as tetrads.It may be related to the less specialized group Jussiaeeae, consisting of the genus Ludwigia (including Jussiaea and Isnardia), which resembles it in having dotlike, heteropycnotic chromosomes; in growing in moist places; and, in many species, in shedding its mature pollen in tetrads.The basic chromosome number of Ludwigia, however, is x = its tetrads are made up of pollen grains that differ greatly from those of Epilobieae and have probably evolved independently (Skvarla et al, 1975); and it lacks interxylary phloem, present in Epilobieae (Carlquist, 1975).Ludwigia seems to be a relatively generalized genus within the family, resembling Fuchsia in its retention of primitive characteristics, as inferred by Eyde & Morgan (1973), and it probably is not directly related to Epilobieae, which then appear as a rather isolated group within the family.Although the fossil record is badly in need of reevaluation, Epilobieae probably extend back to Paleogene time (see discussion in Eyde & Morgan, 1973: Within this tribe, the genera are closely related to one another.This paper is directed to the following question: how many genera and sections, in the sense of Lewis & Lewis (1955) and Raven (e.g., 1963Raven (e.g., , 1969)), is it useful to recognize?Boisduvalia (Raven & Moore, 1965) includes six species of annual plants of western North and South America.Collectively, they are distinguished from 1I am ors, to the U. S. National Science Foundation for a series of grants in support of my study of Onagraceae, to Steven R. Seavey for useful comments on this paper, and to G. Perr: audin for advice on the progress of his hybridization experiments.