Phylogenetic Relationships in Cornus Based on Chloroplast DNA Restriction Sites: Implications for Biogeography and Character Evolution

Abstract

Chloroplast DNA (cpDNA) restriction site analysis was used to elucidate phylogenetic relationships within the taxonomically controversial genus, Cornus. Twenty-nine species representing all major morphological subgroups of the genus were analyzed with 21 restriction endonucleases. Major lineages within Cornus identified by the cpDNA restriction site data are highly concordant with those suggested by both rbcL sequences and morphology. Relationships among these lineages are well-resolved by the restriction site data. The genus diverged early into two major clades: the blue-fruited group bearing blue or white fruits and the red-fruited group bearing red fruits. The blue-fruited clade further comprises two lineages: the alternate-leaved group and the opposite-leaved group. The red-fruited clade is composed of three lineages: the cornelian cherries, the dwarf dogwoods, and the big-bracted dogwoods, with the latter two as sister- groups. The cpDNA restriction site data also correlate closely with the evolution of chromosome number, morphology, and phytochemistry. Most notably, the chromosome number of n = 10 evolved twice in Cornuis, and the small, non-petaloid bracts in C. disciflora apparently represent a reversal to the non-showy state. Furthermore, the presence of iridoids in the red-fruited dogwoods apparently is a retention of the plesiomor- phic condition.