There are a lot of “Arabidopsis relatives”… the Brassicaceae includes nearly 4000 species. About 15% of these have been characterized regarding genome sizes; for about 2000, chromosome numbers are known. The most comprehensive resource for taxonomy, systematics, evolution, and available germplasm resources and specimen collections for the family is BrassiBase; unfortunately, there is no similar resource for the ecological or physiological characteristics of the different species.
Most of the species currently “in use” were selected because tools originally developed for Arabidopsis thaliana work, at least to some extent, with them. They are all small, rapid cycling, and growable in Petri-dishes at lab light levels. And within however many chromosomes they sport, the genes are lined up in identifiable blocks highly similar to A. thaliana.
At this point, only a small fraction of the species could be considered eXtremophytes. But for these, the number of different eXtreme conditions is quite broad. For example, at least two are known for their tolerance of salinity Eutrema salsuginea was originally selected as a model organism because of its ability, in the natural world, to function in saline, cold, and freezing conditions, and for its efficient mobilization of resources in poor or degraded soils. Schrenkiella parvula, on the other hand, was selected because of its ability, in the natural world, to function in the hypersaline conditions surrounding Lake Tuz in central Anatolia, Turkey, and for its tolerance of high levels of other cations, especially Li+ and Mg2+. Little is known about the ecology of this species.
In contrast, the eXtreme plant bona fides of Arabidopsis lyrata stem from its preference for sandy, gravelly, rocky or chasmophytic “soil”. At the molecular level, it is proving to be a valuable tool for understanding of mutation, selection and genome-size transformations in plants.
Often used in comparative studies with A. lyrata, Arabidopsis halleri is a self-incompatible heavy metal hyperaccumulator, especially of cadmium and zinc. Its broad European and Asian distribution also makes A. halleri a useful model for ecological genomics studies, and its interfertility with A. lyrata makes the two species good tools for understanding evolution of heavy metal tolerance.
Beyond these, for which species pages are included in the site or are being constructed, genome resources are currently available for at least 9 other species. In lieu of complete coverage at this point, go to the Genome Resources menu to the left.