White flowered Streps: there are quite a few! I've just taken this picture of Pearl, but it's similar to Albatross, Maasens White and Snow White. So, what's the difference?

While all four Streptocarpus varieties produce elegant white flowers, they differ primarily in their growth habit and flower abundance. Pearl is a modern free-flowering variety with a RHS Recommends Award of Garden Merit, while Albatross is noted for its strong stems and large flowers. Snow White is a more compact, dwarf-like variety (be careful not to overwater!), and Maassen’s White is a classic, large-flowered variety with a pure white appearance.

Back in the middle of the last century, on the nursery of Mr Maassen's in the Netherlands, a white flowered mutant of Streptocarpus ‘Constant Nymph’ appeared. This plant completely lacked the purplish pigment, anthocyanin, found in the flowers and flower stems of ‘Constant Nymph’. Hence the flowers were white, still with the yellow eye of the parent, and the flower stems were green, not purplish.
This plant became known as ‘Maassen’s White’. ‘Maassen’s White’ was treated with x-rays and colchicine, and from it came ‘Albatross’ and ‘Snow White’. ‘Albatross’ is a larger more robust plant in all respects, and is a tetraploid (it has four sets of chromosomes instead of the normal two sets). Colchicine interferes with normal cell division, so that the chromosomes do not separate properly at the first division. ‘Snow White’ is much more compact, with small upturned flowers.