In article , P van Rijckevorsel
wrote:
The advantage of capitalising common names is
clearest when the first part of the name is a common adjective (red, blue,
little, tall, common): in such cases capitalizing, e.g. Tall Fescue makes it
clear that the entire phrase is a name. This as opposed to tall fescue which
could be a tall specimen of fescue.

I agree. A nature reserve I help out on produced a booklet on trees last year.
In that, we capitalised common names but only where they referred to the plant
itself. Thus, for example, "Common Oak" but "an oak bench".

Hope that helps.

Roger