Cytogenetics of Hibiscadelphus (Malvaceae): A Meiotic Analysis of Hybrids in Hawaii Volcanoes National Park

The chromosome number of 2n = 20 II reported here is the first determination for Hibiscadelphus giffardianus Rock and H. distans Bishop & Herbst. An earlier report of the same number for H. hualalaiensis Rock is substantiated. Cytogenetic analysis of H. x puakuahiwi Baker & Allen, a hybrid cross between H. giffardianus and H. hualalaiensis suggests that chromosome pairing and microsporogenesis are not affected in the first generation. However, although chromosome pairing is normal at diakinesis in the seven F 2S analysed, subsequent stages of meiosis and microsporogenesis are severely disturbed and result in the formation of a high percentage of abnormal meiospores in some of the plants. Nevertheless, the apparent lack of hybrid breakdown in two of the F 2 plants and the presence of probable F 3S in one area suggest that gene flow between the two taxa is possible, and, therefore, must be taken into consideration if these two endangered species are to be maintained as distinct entities. MATERIALS AND METHODS Floral bud material for meiotic analysis was fixed in a mixture ofchloroform, absolute ethanol, and glacial acetic acid (6:3:1). Anthers were squashed in acetocarmine and mounted according to Beeks' permanent squash method (Beeks 1955). Slides were examined and photographed with the aid of phase contrast optics. 191 Hibiscadelphus has been collected on the islands of Kauai, Hawaii, and Maui, but, according to Bishop and Herbst (1973), all known wild populations of the five species recognized by them are now extinct or imminently threatened. Fortunately, Hibiscadelphus can be cultivated and has been established in various localities including Kipuka Puaulu and Kipuka Ki in Hawaii Volcanoes National Park. One result of cultivation was the spontaneous production of hybrid seeds where H. giffardianus Rock and H. hualalaiensis Rock were planted close together in Kipuka Puaulu. Park personnel unwittingly collected some of these hybrid seeds from H. giffardianus and planted the propagated hybrid seedlings in various areas of the park with the intention of increasing the numbers of H. J This project was supported in part by contract ex 800060031 from the National Park Service. Manuscript received 30 June 1976. 2 University of Hawaii, Department of Botany, 3190 Maile Way, Honolulu, Hawaii 96822; and Hawaii Volcanoes National Park, Mauna Loa Field Station, Hawaii 96718. giffardianus. Subsequently, park personnel collected seeds from F 1 trees with the same intention ofpropagating more H giffardianus. Accordingly, F 2s were unknowingly cultivated until the existence of the hybrids was detected in 1973 and described by Baker and Allen (1976). The occurrence of these cultivated hybrids (cf. Figure lA) stimulated the present investigation in which it was our intent to characterize the nature and degree of cytogenetic differentiation between H. giffardianus and