CYTOGENETIC IMPLICATIONS OF ARTIFICIAL HYBRIDS BETWEEN THE HAWAIIAN SILVERSWORD ALLIANCE AND NORTH-AMERICAN TARWEEDS (ASTERACEAE, HELIANTHEAE-MADIINAE)

Two vigorous transoceanic, bigeneric hybrids, Dubautia laevigata (n = 14) x Raillardiopsis muirii (n = 8) and [Dubautia knudsenii x laxa] (n = 14) x Madia bolanderi (n = 6), and one vigorous transoceanic trigen eric hybrid, Dubautia scabra (n = 14) x [M. bolanderi x R. muirii], be tween mainland tarweeds and Hawaiian silversword allies were artificia lly produced and subjected to cytogenetic analysis. In addition to uni valents, approximate to 46-80% of the microsporocytes scored from thes e hybrids exhibited from one to four bivalents. However, some of the b ivalents scored in the second bigeneric hybrid represented infragenomi c association of Dubautia chromosomes. Stainable pollen of these hybri ds ranged from 4.4 to 49%, mostly comprising large, tetracolporate, ap parently diploid grains. The functionality of such grains was demonstr ated in the primary hybrid M. bolanderi x R. muirii that was used to p roduce the trigeneric hybrid, and suggests the possible mode of origin of the Hawaiian genome via allopolyploidy. Illustrations of parents a nd F(1)s indicate that the hybrids produced in this study generally ex hibit intermediate character states. However, the phenotypes of the '' ray'' flowers in hybrids between discoid and radiate species were noti ceably unpredictable; in one case intermediacy appeared to be expresse d largely in quantitative terms, while in two others intermediacy appe ared to be expressed largely in qualitative terms.