Saxifrage family, Saxifragaceae
There are two varieties of foamflower in the Eastern United States – var. cordifolia, which occurs in the Catskills and is a running form, producing above ground stolons and slowly forming a groundcover, and var. collina, which occurs from Maryland to Kentucky south to Mississippi and Georgia and is a clumping form. T. cordifolia var. collina is often also listed as T. wherryi in horticulture though that is simply a botanical synonym not a different species.
We generally assign clumping horticultural forms to T. cordifolia var. collina and running horticultural forms to T. cordifolia var. cordifolia, though not all horticultural varieties are straight species and may be hybrids between the two – a western species, T. trifoliata, may also be involved in the parentage of many cultivars.
Updated 12 April 2023