EXPERIMENTAL HYBRIDS IN EPILOBIUM (INCLUDING SECT. ZAUSCHNERIA) SPECIES WITH N = 15 (ONAGRACEAE)

Experimental hybrids involving the three diploid subspecies of Epilobium sect. Zauschneria formed 15 bivalents at meiotic metaphase I, as did experimental hybrids between the three other species of Epilobium (comprising sect. Cordylophorum) with n = 15. The gametic chromosome number of E. suffruticosum Nutt., n = 15, and its relationship to the other two species are reported for the first time. Although we have not obtained hybrids between the species of these two sections, their morphological similarities are impressive and they are surely closely related. LONG REGARDED as a distinct genus, Zauschneria, with its large, orange-red, hummingbird-pollinated flowers is, in fact, closely similar to one group of the genus Epilobium with which it shares many morphological features (Brandegee, 1892; Lewis and Raven, 1961), a similar seed morphology (Seavey, Magill, and Raven, In press), ultrastructural similarities in the pollen and viscin threads (Skvarla, Raven, and Praglowski, 1976; Skvarla et al., In press), and the gametic chromosome number n = 15 (Lewis and Raven, 1961; Kurabayashi, Lewis, and Raven, 1962). A reevaluation of these characteristics in the context of the tribe Epilobieae has led to the incorporation of Zauschneria within Epilobium (Raven, 1977). Clausen, Keck, and Hiesey (1940) conducted an extensive hybridization program involving the taxa of Epilobium sect. Zauschneria, and they recognized three species with a gametic chromosome number of n = 15 and one with n = 30. Hybrids between Epilobium canum subsp. canum and subsp. septentrionale (Keck) Raven were shown to form 15 bivalents at meiotic metaphase (Clausen, 1951), but the cytological relationship of these two entities to the third with n= 15, subsp. garrettii (A. Nels.) Raven, was not studied. The taxa with n = 30 were shown to be directly related to and intergrading with their antecedents with n = 15 (Clausen et al., 1945). In consequence of this pattern, and of the results reported in this paper, we prefer to regard all of these entities as subspecies of a single polymorphic species, Epilobium canum (Greene) Raven (Raven, 1977). 'Received for publication 14 June 1976; revision accepted 7 December 1976. Supported by a series of grants from the U.S. National Science Foundation to Peter H. Raven. We are grateful to T. Mosquin for material of Epilobium suffruticosum and to R. W. Hodges for the determination of moth larvae. The purpose of this paper is to report on the chromosome pairing and fertility of hybrids of all three diploid subspecies of E. canum and to describe the chromosome relationships and fertility of hybrids of the three species of Epilobium most closely related to sect. Zauschneria. Two of the three species of Epilobium sect. Cordylophorum, which with sect. Zauschneria includes all known species of the genus with n = 15, are local endemics-E. nivium T. S. Brandegee in the North Coast Ranges of California, and E. nevadense Munz in the Charleston Mountains of southern Nevada and the Beaverdam Mountains of southwestern Utah (Higgins, 1972). The third species of sect. Cordylophorum, E. suffruticosum Nutt. of Idaho, western Montana, northwestern Wyoming, and possibly eastern Washington, displays more generalized features than any other species of the worldwide genus Epilobium, with some 200 species (Raven, 1977), and is quite distinct from the other two species morphologically. MATERIALS AND METHODS-All hybridizations were performed in an insect-free greenhouse in Bakersfield, California, in 1974. All plants were either grown from seed or transplanted to the greenhouse, with the exception of E. suffruticosum. Pollen of this species was airmailed from Teton National Park, Wyoming. Vouchers of all parents and hybrids are deposited at the Missouri Botanical Garden. The sources of our material were as follows: Epilobium canum subsp. canum: seed from cultivated plants at Rancho Santa Ana Botanic Garden, original parents from near Prisoners Harbor, Santa Cruz I., Santa Barbara Co., Calif. (G844); E. canum subsp. garrettii: transplants from Zion Natl. Park, Washington Co., Utah (G865); E. canum subsp. septentrionale: transplants from U.S. Hwy. 299 near Willow Creek, Humboldt Co., Calif. (G867); E. nevadense: