SEED MORPHOLOGY OF HYDRANGEACEAE AND ITS PHYLOGENETIC IMPLICATIONS

Seed morphology of Hydrangeaceae was explored to describe the paramete rs of diversity, define characters and character states, and hypothesi ze monophyletic groups in the family on the basis of derived features. Eleven seed characters were defined that delimit four basic aspects o f morphology, including (1) shape, (2) primary sculpture, (3) secondar y sculpture, and (4) appendages. Character states could not be delimit ed readily in some aspects of diversity, including transectional shape and length of seeds. Despite continuous variation in seed length, whe n mapped on previous cladograms these data supported the hypothesis th at seeds less than 1.0 mm long were plesiomorphic and that seed size h ad increased separately in different subclades. Seed size increased in association with wing loss in Fendlera, Fendlerella, and Whipplea. A shift from apical, interstylar dehiscence of fruits that produce a ver y limited gap for seed emergence in most members of the hydrangea clad e to fruit wall fragmentation may have permitted an increase of seed s ize in Decumaria, Pileostegia, and Schizophragma. The data help to sup port hypotheses of monophyly for Deutzia and Philadelphus, although re levant character states appear to display parallelisms. The data also help to demonstrate the paraphyly of Hydrangea as traditionally circum scribed. A derived urceolate seed form allies Broussaisia and Dichroa with Hydrangea hirta and Hydrangea luteovenosa, These data indicate th at fossil seeds recognized as Dichroa from the Middle Oligocene of Eur ope may be indistinguishable from those of certain Hydrangea species. Hydrangea heteromalla and Hydrangea paniculata share derived long, spi ndle-form seeds with a flange at the micropylar pole with Decumaria an d Schizophragma, and these taxa may form a monophyletic group that inc ludes Pileostegia. The tropical species of Hydrangea section Cornidia share a derived rarity of anticlinal crosswalls in the seed body. Curr ent phylogenetic hypotheses indicate that the micropylar cowls that Ca rdiandra and Deinanthe share with Deutzia are evolutionary parallelism s. A derived funicular appendage supports prior hypotheses of monophyl y for Fendlerella and Whipplea. These two genera may be most closely r elated to fendlera, with which they share seed coat cells with convex long axes.