Generic delimitations within the Sium alliance (Apiaceae tribe Oenantheae) inferred from cpDNA rps16-5′trnK ^(UUU) and nrDNA ITS sequences

Previous studies of the Sium alliance within Apiaceae tribe Oenantheae, based only on nrDNA ITS sequences, revealed that the genera Sium and Berula may not be monophyletic. To confirm issues of relationships and implement nomenclatural changes, we obtained additional ITS sequences as well as independent data from the cpDNA rps16-5′trnK ^(UUU) region which includes the rps16 intron and the spacer region between genes rps16 and 5′trnK. We examined 78 accessions of tribe Oenantheae including representatives of all 23 species of the Sium alliance (Afrocarum, 1 sp.; Apium pro parte/Helosciadium, 5 spp.; Berula, 1 sp.; Cryptotaenia, 4 spp.; Sium, 12 spp.). Results of Bayesian analysis and maximum parsimony analyses of partitioned and combined data revealed that the Sium alliance is strongly supported as monophyletic. Within this clade, four major subclades are resolved. Three of these subclades comprise species that were traditionally placed in Cryptotaenia, Helosciadium/Apium pro parte, and Sium s.str. (9 spp.). A restitution of the genus Helosciadium, including all Eurasian species of Apium with the exception of A. graveolens, the generitype, is supported by both molecular data and morphology. The fourth subclade, Berula sensu lato, encompasses all representatives of a widely distributed B. erecta, a monotypic African Afrocarum, and three members of Sium from Africa (S. repandum) and Saint Helena (S. bracteatum, S. burchellii). The Sium species from Saint Helena form a sister group to African representatives of B. erecta. The Berula sensu lato clade is recognized at the generic level and these four African/Saint Helena species are transferred into Berula. African and North American populations of B. erecta are distinct from their Eurasian relatives and are therefore proposed to be treated as separate species (B. thunbergii and B. incisa, respectively).