A Phylogenetic Study of Apiaceae Tribe Caucalideae

Abstract

Since the tribe Caucalideae was established for those species of Apiaceae (Umbelliferae) with spines, tubercles or bristly hairs on the primary and/or secondary ridges of the fruits, there has been considerable disagreement as to its proper circumscription, the relationships among its members, and the delimitation of certain genera. Although Heywood and Jury (Heywood, 1982) provided a checklist of Caucalideae, recognizing 21 genera and 68 species, no rigorously constructed estimate of phylogeny exists for these taxa. Phylogenetic relationships within Caucalideae were assessed using nucleotide sequence variation in the internal transcribed spacer (ITS) regions of 18S-26S nuclear ribosomal DNA, detailed restriction site mapping of the chloroplast genome, and morphological and anatomical characters. Evolutionary patterns of selected (i.e., cytological, palynological, phytochemical and morphological) characters were interpreted by plotting their distribution on the ITS-based phylogeny, revealing that many of these characters are highly homoplastic. On the basis of these comparative data, the following results were obtained: (1) Phylogenies derived from three independent lines of evidence are largely congruent, suggesting that hybridization may not have been a factor in the evolution of this group; (2) There is little support for any existing system of classification for the tribe. Aphanopleura, Psammogeton and Kozlovia are excluded from the tribe, whereas representatives from tribe Laserpitieae are included. The genus Chaetosciadium is best treated within Torilis; (3) Fruit primary appendage characters are more useful than those of secondary appendages for delimiting generic boundaries; (4) Tribe Caucalideae sensu lato is provisionally established and consists of subtribes Daucinae (Daucus, Pseudorlaya, Pachyctenium, Agrocharis, Laserpitium, Orlaya, Ammodaucus, Cuminum, Polylophium and Artedia) and Caucalidinae (Astrodaucus, Turgeniopsis, Szovitsia, Torilis, Yabea, Caucalis, Turgenia and Lisaea).