Speedwell is a diverse genus, but all produce delicate spikes of flower in shades of white, blue or purple, over low clumps of foliage.
There are about 250 species, ranging from alpines to marginal aquatics, which are found growing in most temperate regions of the northern hemisphere, especially Europe.
A sunny position with free-draining soil is best for most of the perennial and alpine species. Deadhead regularly to prolong flowering.
Rosy Hardy's blog on Veronicas