analyses of DNA sequence data for the subtribe Banksiinae, which then comprised genera Banksia and Dryandra. Their analyses suggest a phylogeny that differs greatly from George's taxonomic arrangement. B. oligantha resolves as sister taxon (that is, next closest relative) to B. ilicifolia, and B. cuneata resolves as sister to these two. This suggests a monophyletic B. subg. Isostylis; yet the clade appears fairly derived (that it, it evolved relatively recently), implying that B. subgenus Isostylis may not merit subgeneric rank. Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra into it, and publishing B. subg. Spathulatae for the taxa having spoon-shaped cotyledons; thus B. subg. Banksia was redefined as encompassing taxa lacking spoon-shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. oligantha is placed in B. subg. Banksia. Phylogeny Relationships between B. oligantha and the other members of B. subg. Isostylis still remain unclear. Though Mast's studies found B. cuneata to be the most basal of the three species, a 2004 study of genetic divergence within the subgenus yielded both other possibilities: some analyses suggested B. ilicifolia as basal, while others suggested B. oligantha. Further complicating the situation is the southernmost (and closest) population of B. cuneata, which has both genetic and phenetic affinities with B. oligantha. The origin of this population is unknown: it might have arisen through hybridisation, or it may be a transitional or even ancestral form. Finally, biogeographical factors suggest that B. ilicifolia would be the most basal of the three species: it occurs in the High Rainfall Zone where relictual species are most common, whereas the others are restricted to the Transitional Rainfall Zone, where more recently evolved species are most common. Distribution and habitat Banksia oligantha occurs over a range of about in southern parts of the Avon Wheatbelt region of the Southwest Botanical Province of Western Australia. Four populations are known, containing about 1,700 adult plants in total: The first known population, at Wangelling Gully Nature Reserve in Tarwonga. This population appears to be in decline: in 1988 it was estimated as containing from 500 to 800 plants, but a 2001 survey found only 198 adults, 1 seedling, and 286 dead plants; and a 2004 survey found 135 adults, no seedlings, and 174 dead plants. A