Phylogenetic relationships in Cornus (Cornaceae)

Cornus and potential outgroups were surveyed for morphological characters in order to evaluate relationships within the genus. Examination of bract placement and inflorescence development led to a revised interpretation of inflorescence structure. Contrary to previously published reports, all members of subg. Kraniopsis and Mesomora were found to possess inflorescence bracts, albeit small and often caducous prior to anthesis. Nine monophyletic taxa, here treated as subgenera, were initially recognized in Cornus; however, because of character variability within subg. Cornus, Cynoxylon, and Syncarpea, three species were segregated from these original OTU'S and treated as additional OTU'S in a subsequent analysis. Various characters previously used to support putative relationships of Nyssa, Davidia, and Camptotheca with Cornus (transeptal vascular bundles, germination valves, chromosome number, and iridoids) were found to be suspect. The presence of two-armed single-celled trichomes does support the recognition of Cornus, Mastixia, and Diplopanax as a monophyletic group. Previous phylogenetic hypotheses for Cornus were tested in a cladistic analysis of 28 morphological, anatomical, chemical, and cytological characters. Using Mastixia and Diplopanax as outgroups in a simultaneous analysis of ingroup and outgroup relationships, a new hypothesis of phylogeny was generated that is in conflict with previously published works. In this analysis the "cornelian cherries" (subg. Cornus and Afrocrania) and the "big bracted dogwoods" (subg. Discocrania, Cynoxylon, and Syncarpea) are sister groups. The "dwarf dogwoods" (subg. Arctocrania) are sister to them. This phylogeny implies that bract expansion into a showy non-chlorophyllous structure evolved twice in the genus. Three characters unite Cornus as a monophyletic group: dorsal raphe, two or more locules per fruit, and calcium carbonate ornamentation of the trichomes. Two species, C. sessilis and C. nuttallii, were not clearly placed into subgenera and should receive careful scrutiny in future analyses. Cornus subg. Yinquania (comb. et stat. nov.) is recognized here at a new rank, its two species having previously been considered either as members of subg. Kraniopsis, or as the segregate genus Yinquania. It is placed in the proposed phylogenetic scheme as the basal clade in Cornus.