RELATIONSHIPS AND EVOLUTION OF HYDRANGEACEAE BASED ON RBCL SEQUENCE DATA

Phylogenetic analyses of rbcL sequences were used to address both syst ematic and evolutionary questions posed by the angiosperm family Hydra ngeaceae. Our analyses suggest the presence of a monophyletic Hydrange aceae most closely allied with Loasaceae, a finding in agreement with other molecular as well as morphological analyses. Molecular data indi cate that Hydrangeaceae comprise Decumaria, Pileostegia, Schizophragma , Hydrangea, Dichroa, Broussaisia, Platycrater, Cardiandra, Deinanthe, Carpenteria, Philadelphus, Deutzia, Fendlerella, Whipplea, Fendlera, Jamesia, and the enigmatic Kirengeshoma. A particularly close relation ship of Kirengeshoma and Deutzia is indicated. Analysis of rbcL sequen ces suggests that Fendlera and Jamesia are sister to the remainder of the family, lending support to the hypothesis that at least some Carpe nterieae are basal in the family and that Hydrangeaceae may have origi nated in xeric habitats. If this phylogenetic placement of Jamesia and Fendlera is correct, the rbcL trees also suggest that the level of ep igyny has decreased in these genera, as well as in the Fendlerella- Wh ipplea clade and Carpenteria when compared to the outgroup taxa, which are wholly epigynous. Furthermore, the rbcL trees support proposed ev olutionary trends in wood anatomy, suggesting, for example, that uplan d tropical taxa have evolved longer vessel elements with more numerous bars on scalariform perforation plates. The xerophytic basal members of Hydrangeaceae, like the closely related Loasaceae, have short, narr ow vessel elements with scalariform perforation plates bearing few bar s. Following Jamesia and Fendlera, the remaining hydrangeoids are divi ded into two large subclades that closely parallel the traditional div ision of the family into Philadelpheae and Hydrangeae. Both rbcL seque nces and morphological data suggest close relationships between: 1) Fe ndlerella and Whipplea; 2) Decumaria, Pileostegia, and Schizophragma; 3) Carpenteria and Philadelphus; 4) Deinanthe and Cardiandra; 5) Dichr oa, Broussaisia, and Hydrangea macrophylla. Molecular and morphologica l data also concur in demonstrating that the large genus Hydrangea is not a monophyletic assemblage.