Phylogenetic analyses of ITS and rbcL DNA sequences for sixteen genera of Australian and New Zealand Brassicaceae result in the expansion of the tribe Microlepidieae

Heenan PB, Goeke DF, Houliston, GJ, Lysak MA

Taxon 61: 970-979.


Sequence data from the internal transcribed spacer (ITS) nrDNA and rbcL cpDNA regions were used to determine relationships of genera of Brassicaceae from Australia and New Zealand (NZ) that were previously unassigned to a tribe. Maximum likelihood analysis of 71 ITS sequences identified a monophyletic clade of Australian genera, including Carinavalva and Microlepidium that had previously been assigned to the tribe Microlepidieae. Pachycladon is not supported as monophyletic, comprising a clade of the NZ species and another clade of the Tasmanian P. radicatum. These two Pachycladon clades form a polytomy with the Australian clade. Maximum likelihood analysis of the rbcL region generally supports the ITS analysis with the Australian genera forming a monophyletic clade with Pachycladon. Arabidella is polyphyletic in the rbcL phylogeny as A. eremigena is member of the Australian clade but A. trisecta is placed in a sister clade that comprises mainly genera of tribe Camelineae. As a result of these phylogenetic analyses the tribe Microlepidieae is expanded and now includes 16 genera and 56 species endemic to Australia and New Zealand. Genera included in the Microlepidieae are Arabidella, Ballantinia, Blennodia, Carinavalva, Cuphonotus, Drabastrum, Geococcus, Harmsiodoxa, Irenepharsus, Menkea, Microlepidium, Pachycladon, Pachymitus, Phlegmatospermum, Scambopus and Stenopetalum. Whole-genome duplication has previously been shown to have occurred in the ancestry of Arabidella, Ballantinia, Pachycladon and Stenopetalum and is likely to be a defining feature of the tribe Microlepidieae. Future research needs to investigate circumscription of the Australian genera as there is a predominance of closely related monotypic genera in the Microlepidieae. With resolution of the tribal placement of these Australian and New Zealand genera, ca. 94% (302) of the 321 genera in the family have been assigned to a tribe.