Tiarella stolonifera is a species of flowering plant in the family Saxifragaceae. The specific name stolonifera means "spreading by stolons", an important characteristic of this species (not to be confused with Tiarella austrina, which also spreads by stolons). Known as the creeping foamflower, it has the widest range of any species of Tiarella in eastern North America.
Description
Tiarella stolonifera is a perennial, herbaceous plant with a short, slender rhizome. It has a leafless flowering stem and relatively small basal leaves without an extended terminal lobe. Most importantly, the species has the ability to produce stolons.
The heart-shaped basal leaves of Tiarella stolonifera resemble those of species in other genera. For example, T. stolonifera is sometimes confused with Mitella diphylla, a closely related species that occurs over a similar range and habitat. If a plant lacks sufficient evidence of flowering, the orientation of the hairs on the basal leaf stalk may be used to distinguish the two species. T. stolonifera has dense spreading hairs (outward-facing, angled 90 degrees) of various lengths while M. diphylla has long retrorse hairs (backward-facing, angled 45 degrees or less) sparsely distributed along its basal leaf stalk.
Identification
To positively identify Tiarella stolonifera, all of the following key features must be verified (in any order):
Stolon present
Basal leaves usually about as long as wide
Basal leaf lobes usually obtuse to rounded with the terminal lobe not extended
Flowering stem without leaves or foliaceous bracts
The key features listed above are similar to those of Tiarella cordifolia but the presence of a stolon rules out that species.
Taxonomy
In 1937, Olga Lakela split Tiarella cordifolia sensu lato into two mutually exclusive groups, one with stolons and one without. She described two varieties of Tiarella cordifolia (var. typica and var. austrina) to represent the northern and southern varieties (resp.) of the group with stolons. However, the name Tiarella cordifolia var. typica was invalidly published.
Guy Nesom likewise split Tiarella cordifolia sensu lato into two groups based on stolons in 2021. In particular, he described Tiarella stolonifera, a northern species with stolons, and Tiarella austrina, the corresponding southern species based on Lakela's variety.
In 1917, Oliver Atkins Farwell described a variety of Tiarella cordifolia sensu lato with a small bract on the flower stem. Farwell's type specimen did not include a stolon, but since it was collected in Michigan, Tiarella cordifolia var. bracteata is considered to be a synonym for Tiarella stolonifera . The occasional plant with a leafy flowering stem found throughout the range of the species is not to be confused with Tiarella austrina, a distinct species that has both a stolon and stem leaves.
Distribution and habitat
Tiarella stolonifera has the widest range of any Tiarella species in eastern North America, from Wisconsin across the eastern half of the Great Lakes region into the northeastern United States and adjacent Canada, and from there, south into Kentucky, Virginia, Tennessee, and North Carolina. It is the only species of Tiarella in the following 17 provinces and states:
Canada: New Brunswick, Nova Scotia, Ontario, Québec
United States: Connecticut, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, West Virginia, Wisconsin
Tiarella stolonifera and at least one other species of Tiarella are found in five (5) additional states. Relevant counties include:
Kentucky: Bell, Carter, Clay, Elliot, Estill, Floyd, Gallatin, Garrard, Greenup, Harlan, Jackson, Jessamine, Jefferson, Johnson, Kenton, Knott, Knox, Laurel, Lee, Leslie, Letcher, Lincoln, Madison, Martin, McCreary, Menifee, Perry, Pike, Powell, Pulaski, Rockcastle, Rowan, Whitley, Wolfe, Woodford Maryland: Allegany, Garrett, Harford, Washington North Carolina: Alleghany, Ashe, Avery, Buncombe, Burke, Madison, McDowell, Mitchell, Watauga, Wilkes, Yancy Tennessee: Anderson, Campbell, Carter, Claiborne, Grainger, Greene, Hancock, Hawkins, Knox, Morgan, Roane, Scott, Unicoi, Union, Washington Virginia: Bath, Bland, Buchanan, Carroll, Dickenson, Floyd, Giles, Grayson, Highland, Pulaski, Rockbridge, Rockingham, Russell, Scott, Smyth, Tazewell, Washington, Wise, Wythe