These plants produce clumps of grass-like or sword-shaped foliage and small starry flowers in low clusters or tall spikes, usually in shades of blue or yellow.
There are about 100, mainly perennial, species, which grow in a variety of habitats from rocky slopes to moist meadows. Most come from North and South America, with just one variety native to Ireland.
They grow best in full sun, with free-draining soil. Winter waterlogging will not be not tolerated.