Evolutionary Biology of Trillium and Related Genera (Trilliaceae) : II. Cladistic Analyses on Gross Morphological Characters, and Phylogeny and Evolution of the Genus Trillium

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Cladistic analyses were conducted based upon 22 gross morphological and one floral odor characters for 42 Trillium species, one Kinugasa, one Daiswa, and two Paris species of the Trilliaceae, using Daiswa and Paris as outgroups. The cladistics provided an informative result with regard to the affinity and phylogeny of the taxa referred to the genus Trillium and related genera in the Trilliaceae, suggesting that Trillium is composed of four major infrageneric groups : (1) the pedicellate-flowered group represented by the Erectum group including 13 species, (2) the Undulatum group, a loosely clustered paraphyletic group including five species, (3) the Govanianum group consisting of only two species, and (4) the Sessile group including 22 species. The monophyly of the Sessile group is very evident. The results are concordant with the earlier results of the RFLP analysis of cpDNA conducted by us. It is noteworthy, however, that the pedicellate-flowered group of Trillium is not simply monophyletic, as was assumed previously, but instead consists of at least three to four distinct groups as noted above. The implications and limitations of using distantly related genera, such as Daiswa or Paris as outgroups, in the cladistic analysis were also argued.
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