Systematics of Spilanthes (Compositae: Heliantheae)

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Abstract
Spilanthes is widespread throughout the New and Old World tropics. Morphological and chromosomal evidence supports separation of the genus into two genera, Spilanthes and Acmella, which can be distinguished by at least eight morphological characters and by distinctive basic chromosome numbers. Studies of other genera within the Heliantheae suggest that both Spilanthes and Acmella are allied to Salmea in the Verbesininae. Spilanthes is here recognized as comprising six species distributed primarily in sandy soils of South America, the West Indies, northern Australia, Malaysia, and central and western Africa. A phylogenetic reconstruction employing cladistic methods suggests that the New World species, S. leiocarpa, S. nervosa, S. paraguayensis, and S. urens, are more closely allied to each other than to the Old World species. The cladistic analysis further suggests a closer relationship between the Australo-Malaysian S. anactina and the New World species than with S. costata, a species restricted to central and western tropical Africa.