Seed Morphology of Hydrangeaceae and Its Phylogenetic Implications

Abstract

Seed morphology of Hydrangeaceae was explored to describe the parameters of diversity, define characters and character states, and hypothesize monophyletic groups in the family on the basis of derived features. Eleven seed characters were defined that delimit four basic aspects of morphology, including (1) shape, (2) primary sculpture, (3) secondary sculpture, and (4) appendages. Character states could not be delimited readily in some aspects of diversity, including transectional shape and length of seeds. Despite continuous variation in seed length, when mapped on previous cladograms these data supported the hypothesis that seeds less than 1.0 mm long were plesiomorphic and that seed size had 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 very limited gap for seed emergence in most members of the hydrangea clade to fruit wall fragmentation may have p...