A chloroplast phylogeny ofArisaema(Araceae) illustrates Tertiary floristic links between Asia, North America, and East Africa

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Abstract
The evolution ofArisaemais reconstructed, based on combined sequences (2048 aligned bases) from the chloroplasttrnLintron,trnL‐trnFspacer, andrpl20‐rps12spacer obtained for species from all 11 sections, including sectional type species and geographically disjunct East African and North American/Mexican species. Analyses were rooted with a representative sample of the closest outgroups,PinelliaandTyphonium, to rigorously test the monophyly ofArisaema. Sections inArisaemaare mostly based on leaf, stem, and inflorescence characters and, with one exception, are not rejected by the molecular data; however, statistical support for sectional relationships in the genus remains poor. SectionTortuosa, which includes eastern North AmericanA. dracontiumand MexicanA. macrospathum, is demonstrably polyphyletic. The third New World species,A. triphyllum, also occurs in eastern North America and groups with a different Asian clade than doA. dracontium/A. macrospathum. The genus thus appears to have entered North America twice. Fossil infructescences similar to those ofA. triphyllumare known from approximately 18 million‐year‐old deposits in Washington State and can serve to calibrate a molecular clock. Constraining the age ofA. triphyllumto 18 million years (my) and applying either a semiparametric or an ultrametric clock model to the combined data yields an age of approximately 31–49 my for the divergence ofA. dracontium/A. macrospathumfrom their Asian relatives and of 19–32 my for the divergence between AfricanA. schimperianumand a Tibetan/Nepalese relative. The genus thus provides an example of the Oligocene/Miocene floristic links between East Africa, Arabia, the Himalayan region, China, and North America. The phylogeny also suggests secondary loss of the environmental sex determination strategy that characterizes all arisaemas except for two subspecies ofA. flavum, which have consistently bisexual spathes. These subspecies are tetraploid and capable of selfing, while a third subspecies ofA. flavumis diploid and retains the sex‐changing strategy. In the molecular trees, the sex‐changing subspecies is sister to the two non‐sex‐changing ones, and the entire species is not basal in the genus.
Funding Information
  • University of Missouri System