Taxonomic studies ofAsarum sensu lato |
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Authors: | Takashi Sugawara |
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Institution: | (1) Makino Herbarium, Faculty of Science, Tokyo Metropolitan University, Setagaya, 158 Tokyo |
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Abstract: | The floral vascular anatomy of 12 species representing each ofAsarum s. str.,Asiasarum, Geotaenium, Heterotropa andHexastylis are compared to clarify intergeneric relationships. The five genera have basically similar structures in floral morphology
and vasculature, and consistently have a six-carpelled compound ovary and the associated similar placental vasculature. They
show, however, a significant difference in the position and the constituent of the “ventral” carpellary bundles in the placental
axis betweenAsiasarum-Heterotropa-Hexastylis andAsarum-Geotaenium. InAsiasarum, Heterotropa andHexastylis the ventral bundles of each carpel are basically free and antilocular as expected in the least specialized compound ovary
of angiosperms; in contrast, inAsarum andGeotaenium the ventral carpellary bundles are antiseptal and heterogenous (i.e., formed by the lateral fusion of ventral bundles of
adjacent carpels). Shared probable apomorphic floral vasculature, as well as shared single style-column, suggests the closest
mutual relationships betweenAsarum andGeotaenium. In terms of floral morphology and anatomy,Asiasarum, Heterotropa andHexastylis retain plesiomorphies. Possible chromosomal evolution in the related genera is also discussed. |
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Keywords: | Aristolochiaceae Asarum Floral anatomy Heterotropa Taxonomy |
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