Following up on the origins of RESTIOS I came across this Wikipedia article - explains the diversity of soil-types of the Cape Flora.
So much I never knew.
This is where I started: RESEARCH PAPER
Rare species, Restionaceae, and the Cape flora
[Hans Peter Linder
First published: 27 September 2019
Range size variation in the restios is largely driven by history (expressed as the distance from the Kogelberg region), suggesting that the Kogelberg region may have been most climatically stable during the Neogene and Pleistocene. The second-most important driver is the environment (i.e. rock type, elevation, rainfall), generally with spatially restricted habitats hosting range-restricted species…
The Kogelberg area has the steepest and highest drop directly into the ocean of any southern African coastal stretch.
The mountains are made predominantly of Table Mountain Sandstone and form some very rugged terrain, which is extremely rich in fynbos, the native Cape flora.
The Elgin Valley’s surrounding mountain ranges are considered the hub of the Cape floral kingdom. They contain more plant species than anywhere else in the floral region.