Systematics and Evolution of the tribe Arabideae with special emphasis on the genus Arabis (Brassicaceae)
Final Report Abstract
The broadly defined genus Arabis from the Brassicaceae family has been revised systematically only in few parts. Some species previously assigned to Arabis are now confined to genera such as Turritis, Pseudoturrits, Boechera or Fourraea. Other genera such as Arabidopsis/Cardaminopsis or Borodinia have been erroneously placed into Arabis in the past. Some of the above mentioned genera are not members of tribe Arabideae, and considering the actual taxonomic treatments approximately 88 Arabis species together with approximately 400 species of the genus Draba and its closest relatives might represent the core of tribe Arabideae. Based on our work we circumscribed 17 genera in total within the tribe Arabideae, and finally leaving Arabis as paraphyletic taxon indicating the need for further comprehensive taxonomic adjustments. We made some first steps towards this direction and described three new genera, namely Scapiarabis, Sinoarabis and Borodinopsis. Our phylogenetic work provides a reliable and robust evolutionary hypothesis enabling us to test principle questions of crucifer evolution. Geographic istribution and colonization patterns indicate tremendous past success of various clades in Arabideae. Consequently, the question arises if there are traits and characters obviously correlated with colonization and diversification. It is intriguing that, when superimposed on the phylogenetic trees, the patterns of life cycle and habitat elevation are almost congruent, especially for all nodes that diverged during the early phases in the evolution of Arabideae in the Mid Miocene. This close correlation between lifecycle strategy and preferred habitat elevation expands the previously raised idea of the pattern of sister relationships between species-poor, annual clades and a larger group of predominantly perennial species. In addition, the perennial species are prevalent in high montane to alpine elevations, whereas the annual species mainly occur in lowland habitats. The results from tribe Brassicaceae highlight some general patterns of crucifer evolution. Speciation rates are mostly high and the evolutionary history of many clades is characterized by multiple radiation events. Interestingly these results are also correlating with spatio-temporal patterns. Reconstructions of past geographical patterns revealed that all early diversification events in Arabideae date to the Mid and Late Miocene and took place in the (western) Irano-Turanian floristic region and/or the (eastern) Mediterranean. Anatolia and the Levantine coast, in particular, is included as the most likely ancestral area for almost all nodes, whereas the Western Mediterranean, the Caucasus and the Iranian mountains are indicated as potential centres of origin with lower frequencies. These early diversification events gave rise to all of the presently existing clades and their respective stems.
Publications
-
(2010) Colonizing the American continent - Systematics of the genus Arabis in North America (Brassicaceae). Amer. J. Bot. 97: 1040-1057
Koch MA, Karl R, Kiefer C, Al-Shehbaz IA
-
(2011) Nomenclatural adjustments in the tribe Arabideae (Brassicaceae). Plant Diversity and Evolution 129: 71-76
Al-Shehbaz I.A., German D.A., Karl R., Jordon-Thaden I., Koch M.A.
-
(2011) The importance of Anatolian mountains as the cradle of global diversity in Arabis alpina L., a key arctic–alpine species. Annals of Botany 108: 241-253
Ansell SW, Stenoien HK, Grundmann M, Russel SJ, Koch Ma, Schneider H, Vogel JC
-
(2012) Systematics and evolution of arctic-alpine Arabis alpina L. (Brassicaceae) and its closest relatives in the eastern Mediterranean. American Journal of Botany 99: 778-794
Karl R., Kiefer C., Ansell S., Koch M.A.
-
(2012) Systematics, taxonomy and biogeography of three new Asian genera from the Brassicaceae, tribe Arabideae: An ancient distribution circle around the Asian high mountains. TAXON 61: 955-969
Koch M.A., Karl R., German D.A., Al-Shehbaz I.A.
