George,
I am also growing Cunonia capensis, although it is relatively young,(less than a year old), and also doing very well with no frost protection here in Berkeley and Richmond. I also saw it growing in habitat on Table Mountain, where it primarily grew in protected shaded ravines immune to brush fires, and grew very tall much like Tanbark Oaks or Umbellaria do in similar conditions. I think this tree also has potential being hedged, as the new growth is so interesting and colorful. Cape Town's climate is more similar to San Diego than San Francisco, so I don't know what its ultimate cold hardiness would be, I would protect it from frosts much colder than 28/29F myself.

Greyia is doing very well in Strybing Arboretum, I think it just needs full sun and good drainage, and obviously will grow faster if placed in a warmer, wind protected spot that heats up. If I recall correctly, this is a late fall into winter bloomer here, so the flowers may not last in a freeze situation. This has survived freezes in Golden Gate Park down to 24/25F, but I don't recall if it froze back to the roots or not in the 1990 and 1998 freezes.

The others I am not familiar with, could you describe what they are and where in South Africa they are native? This might help with getting replies on their hardiness.

thanks for the response---rapanea seems to a component of sheltered moist forest especially at higher elevations (afro-montane)and laurophyllus (a relative of poison oak though apparantly not an irritant)grows on wooded hill slopes and along stream banks (according to Palgrave's "Trees of Southern Africa")in the southeast of the country apparantly near the coast(near the "garden route" and/or the Knysna forest east of the Cape????)---was listed as zone 8 by silverhill but have no altitude stats or further habitat descriptions to make any guesses as to actual hardiness to cold or heat. both are handsome plants with laurel-like leaves and as mentioned previously seem to tolerate cool moist conditions of a northwest winter.