Cultivars
'Album'
This vigorous herbaceous perennial grows to 500 mm (20 in) tall by 600 mm (24 in) wide with spreading rhizomes forming a compact mounded habit. It has soft mid-green foliage and produces small white flowers in clusters during summer above the foliage. 

This tough plant tolerates cold exposed positions in full sun or semi-shade and will grow in most well-drained moist soils including chalky alkaline and heavy clay. It is planted along the front borders and used as a ground cover or planted in patio pots and planter boxes preferring a cool moist position. It grows in USDA zones 4-9.

'Mayflower'
This vigorous herbaceous perennial grows to 750 mm (30 in) tall by 600 mm (24 in) wide with mid-green foliage forming a low spreading habit. During early summer it produces larger violet blue saucer-shaped flowers with white centres that are up to 35 mm (1⅜ in) wide and appear in a small cluster above the foliage. 

This native to the UK grows in well-drained to boggy soil in a semi-shaded to sunny position and is a frost tolerant but drought tender. It grows in USDA zones 4-9.