Tiarella trifoliata, the three-leaf foamflower, is a
species of
flowering plant in the
familySaxifragaceae.[6] The specific name trifoliata means "having three leaflets",[7] a characteristic of two of the three recognized varieties. Also known as the laceflower or sugar-scoop,[8] the species is found in shaded, moist woods in western
North America.
Description
Tiarella trifoliata is a
perennialdicotyledonousherb that flowers in the late spring. The
flowers are bell-shaped, white and solitary forming an elongated, leafless
panicle. The calyx lobes are 1.5–2.5 mm and petals are 3–4 mm. Basal
leaves are 15–80 mm long and up to 120 mm wide,
trifoliate or palmately 3- to 5-lobed. Cauline leaves are infrequent and much smaller.[9]
The typical variety of Tiarella trifoliata (var. trifoliata) has
petiolate leaves with three leaflets per leaf (i.e.,
trifoliate). The cut-leaved foamflower (var. laciniata) also has trifoliate leaves with petioles, but unlike the typical variety, it has deep lobes more than half the length of the leaflet. The one-leaf foamflower (var. unifoliata) has
sessile,
simple leaves (rarely trifoliate).[6]
Taxonomy
Tiarella trifoliata was first described by the Swedish botanist
Carl Linnaeus in 1753.[2] Its
type specimen was collected by
Georg Steller on Cape St. Elias, Kayak Island, Alaska in 1742, but that specimen is now lost. A specimen collected from Sitka, Alaska has been designated as the
neotype for this species.[10]
In 1832,
William Hooker described two additional species of Tiarella in western North America (T. laciniata and T. unifoliata),[11][12] including two hand-drawn illustrations in his description.[13][14]John Torrey and
Asa Gray recognized all three species (T. trifoliata, T. laciniata, T. unifoliata) in their treatment of genus Tiarella in 1840.[15]
In 1905,
Per Axel Rydberg described T. californica based on an earlier description of a species thought to belong to genus Heuchera.[16] All four species (T. trifoliata, T. laciniata, T. unifoliata, T. californica) were included in a taxonomy proposed by
Olga Lakela in 1937.[17]
Based on Hooker's species description,
William Efner Wheelock renamed T. laciniataHook. as a variety of Tiarella trifoliata (var. laciniata) in 1896.[18] Similarly,
Federico Kurtz renamed T. unifoliataHook. as Tiarella trifoliata var. unifoliata in 1894.[19]Flora of North America recognized the varieties (var. laciniata and var. unifoliata) in an influential treatment of genus Tiarella published in 2009.[20] As of October 2022[update], the varieties (not the species) are widely recognized:[6][21][22][1][23][24][25]
Tiarella trifoliataL.
Tiarella trifoliata var. laciniata(Hook.) Wheelock (synonym: T. laciniataHook.)
Tiarella trifoliata var. trifoliata
Tiarella trifoliata var. unifoliata(Hook.) Kurtz (synonym: T. unifoliataHook.)
Likewise Tiarella californica(Kellogg) Rydb. is considered to be a synonym of T, trifoliata var. laciniata.
Distribution
In western North America, Tiarella trifoliata prefers shaded, moist, sometimes dense woods up to 1,900 m (6,234 ft).[6] It ranges from northern
California through western
Canada northward to
Alaska, and eastward to
Montana.[22][26][27] Within this region, the varieties of T. trifoliata have overlapping ranges:
Tiarella trifoliata var. laciniata:[3] British Columbia; Oregon, Washington
Tiarella trifoliata var. trifoliata:[4] Alberta, British Columbia; Alaska, California, Idaho, Montana, Oregon, Washington
Tiarella trifoliata var. unifoliata:[5] Alberta, British Columbia; Alaska, California, Idaho, Montana, Oregon, Washington
T. trifoliata var. trifoliata and T. trifoliata var. unifoliata range north to Alaska, while T. trifoliata var. laciniata only ranges as far north as
Vancouver Island in British Columbia.[28]
Conservation
The conservation status of Tiarella trifoliata is globally secure (G5).[1] Each variety is secure as well.
^USDA, NRCS (n.d.).
"Tiarella trifoliata". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 12 October 2022.
^"Tiarella trifoliataL.". E-Flora BC: Electronic Atlas of the Plants of British Columbia. 2020. Retrieved 9 October 2022.
^"Tiarella trifoliata". State-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014. Retrieved 11 October 2022.
^"Tiarella trifoliata". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014. Retrieved 2 November 2022.
^Pojar, Jim; MacKinnon, Andy. Plants of the Pacific Northwest Coast. Lone Pine Publishing, 1994, p. 168,
ISBN978-1-55105-040-9
Bibliography
Lakela, Olga (1937). "A monograph of the genus TiarellaL. in North America". Amer. J. Bot. 24 (6): 344–351.
doi:
10.1002/j.1537-2197.1937.tb09109.x.
Torrey, John; Gray, Asa (1840).
Flora of North America, Volume 1. New York: Wiley & Putnam. pp. 1–711. Retrieved 25 October 2022.