Phylogenetic relationships of Thlaspi s.l. (subtribe Thlaspidinae, Lepidieae) and allied genera based on chloroplast DNA restriction-site variation

Abstract

Chloroplast DNA restriction-site variation was analyzed in 30 accessions representing 20 species from the major lineages in Thlaspi s.l. (previously described as genera by Meyer 1973, 1979) and allied genera from the subtribe Thlaspidinae (Peltaria, Teesdalia, Cochlearia, Ionopsidium, Aethionema). A total of 161 variable restriction sites were detected. Phylogenetic analyses indicated a division of Thlaspi s.l. into three groups consistent with Meyer's genera Thlaspi s. str., Microthlaspi and Noccaea/Raparia. The genus Thlaspi s.l. as currently described proved to be paraphyletic because one of its major lineages, i.e. Thlaspi s. str., appeared to be more closely related to other genera (Peltaria, Teesdalia) than to the remaining lineages of Thlaspi s.l., i.e. Noccaea/Raparia and Microthlaspi. Sequence divergence values (100 x p) between the Thlaspi s.l. lineages were similar to values between these groups and related genera (Teesdalia, Peltaria), respectively. Chloroplast DNA variation was also used to assess subtribal classification of the genera studied. The cpDNA data were inconsistent with the controversial taxonomic classifications based on morphology. The molecular data would suggest that (1) the subtribe Thlaspidinae, as traditionally described, is not monophyletic; (2) the Thlaspidinae should be reduced to a group consisting of Thlaspi s. str., Peltaria, Teesdalia, Microthlaspi, Noccaea/Raparia, and that Aethionema should be excluded from the Thlaspidinae; and (3) Cochlearia and Ionopsidium represent the subtribe Cochleariinae.