Description
Saxifrage family (Saxifragaceae)
In 2021 a major revision of Tiarella appeared in a study by Guy Nesom (most easily accessible at Wikipedia). The taxon which occurs throughout the northeast has been renamed T. stolonifera (formerly T. cordifolia var. cordifolia). I think most running forms of foamflower available in horticulture are selections of this newly-named taxon. There is a southern running form of foamflower (T. austrina), but it has sharply-lobed leaves with the terminal lobe prominently extended . Off the top of my head I can’t think of any horticultural varieties that run with such foliage.
There are clumping forms of foamflower in the horticultural trade, thought to be straight species, and usually assigned to one of two superseded taxa, either T. cordifolia var. collina or T. wherryi. However, most of the plants we’ve obtained have foliage about as long as wide and so now should likely be assigned to T. cordifolia sensu stricto, the type form of foamflower named by Linnaeus. This will lead to considerable confusion in horticulture because running forms in horticulture are usually named “T. cordifolia” and clumping forms “T. wherryi“. Now the respective names shoud be “T. stolonifera” and “T. cordifolia” – that switching of “T. cordifolia” from a running form to a clumping form will be a considerable challenge for growers and gardeners alike.
Most of the clumping forms of foamflower so popular in the nursery trade however are not simple selections of what is now T. cordifolia but are likely hybrids amongst the various species of southeastern foamflower, though exactly which species are involved with any particular variety is essentially unknowable at this point in time; a western species, T. trifoliata, has also been involved in the parentage of many cultivars. So we list most clumping cultivars as “Tiarella ×” indicating their likely, but unknown hybrid origin.
Updated 2 January 2025
