The new paper concerning Southern African succulents of tribe Senecioneae have been published by Russian botanists in the Journal of General Biology (http://elementy.ru/genbio/abstracts?artid=404). At this Website you can also find more materilas in the field of biogeography including the short abstacts of papers.
Authors of abovementioned paper explain the differences in adaptation and distribution of different phylums by Gause's law of competitive exclusion and different time of expansion on the territory. Besides this data don't explain the predisposition of some Senecioneae phylums to some specific adaptations. According to this it will be interesting to do comparative analysis of plant traits within different taxa and find out the environmental factors limiting them.