A FULLY FERTILE INTERGENERIC HYBRID DERIVATIVE FROM ARGYROXIPHIUM-SANDWICENSE SSP MACROCEPHALUM X DUBAUTIA-MENZIESII (ASTERACEAE) AND ITS RELEVANCE TO PLANT EVOLUTION IN THE HAWAIIAN-ISLANDS

Achenes collected from natural putative F-1 intergeneric hybrids invol ving Argroxiphium sandwicense DC. ssp. macrocephalum (A. Gray) Meyrat and Dubautia menziesii (A. Gray) Keck were germinated and grown in cul tivation, One of these apparent B-1 hybrids that approached D. menzies ii in morphology exhibited greatly increased fertility over the F-1 (7 9% vs. 9% pollen stainability), and was used as a female parent to gen erate a B? progeny by backcrossing a second time to D. menziesii. The B, was surprisingly uniform. One individual that flowered was fully fe rtile (99% pollen stainability). Its floral and vegetative features we re extremely similar to those of the recurrent parent, D. menziesii. O bservations suggest that plants of similar origin may exist under natu ral conditions and that the close relatives, D. platyphylla (A. Gray) Keck and D. dolosa (Degener & Sherff) G. Carr, may have originated fro m the same or a similar intergeneric hybrid combination. Because many other analogous situations occur in the silversword alliance and elsew here in the Hawaiian flora, it is concluded that hybridization is an e volutionarily important phenomenon, especially in unstable geological systems, Although the Hawaiian archipelago is a premier example of suc h instability. continents are not immune to natural perturbations. The refore, hybridization, as a mechanism that greatly extends the size: o f gene pools available for recombination, should also be expected to p lay an important evolutionary role in continental floras.