Comparative morphology of seeds of four closely related species of Aristolochia subgenus Siphisia (Aristolochiaceae, Piperales)

The primary purpose of this study was to determine whether morphological divergence has occurred in seeds of species in a subclade of Aristolochia subgenus Siphisia. Thus, we compared seed mass, surface area, and wings (presence or absence), embryo shape and state, and embryo length to seed length (E:S) ratio in A. californica Torr., endemic to California, A. macrophylla Lamk. and A. tomentosa Sims of eastern USA, and A. manshuriensis Komarov of eastern Asia. We also compared capsule length and number of seeds per capsule in the three US species. All four species have linear, underdeveloped embryos, but for the other morphological features statistically significant differences occurred among the taxa. However, none of the seed morphological features differed between the eastern North American species A. macrophylla and its eastern Asian sister species A. manshuriensis.