''Tiarella'', the foamflowers, is a genus of flowering plants in the family Saxifragaceae. The generic name ''Tiarella'' means "little turban", which suggests the shape of the seed capsules. Worldwide there are seven species, one each in eastern Asia and western North America, plus five species in eastern North America. , the taxonomy of ''Tiarella'' in eastern North America is in flux.

Description

Plants of genus ''Tiarella'' are perennial, herbaceous plants with short, slender

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

s. Three morphological features are used to distinguish ''Tiarella'' species: 1) presence or absence of

stolon In biology, stolons (from Latin '' stolō'', genitive ''stolōnis'' – "branch"), also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external s ...

s; 2) size and shape of

basal leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

; and 3) presence or absence of stem leaves (also called

cauline leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

). Two species of ''Tiarella'' have stolons (''T. austrina'', ''T. stolonifera'') while two other species have stem leaves (''T. nautila'', ''T. austrina''). Plants from the southern Blue Ridge Mountains and southward have relatively large basal leaves with an extended terminal lobe (''T. austrina'', ''T. nautila'', ''T. wherryi''). The following identification key was published by

Guy Nesom Guy L. Nesom (born August 2, 1945)''U.S. Public Records Index'' Vol 2 (Provo, UT: Ancestry.com Operations, Inc.), 2010. is an American writer and botanist. Nesom received his Ph.D. in systematic botany from the University of North Carolina in 19 ...

in 2021:

Taxonomy

In 1753, Swedish botanist Carl Linnaeus established genus ''Tiarella'' by recognizing two species, ''Tiarella cordifolia'' and ''Tiarella trifoliata''. A third species, ''Tiarella polyphylla'', was described by David Don in 1825. Together these three species form the taxonomic backbone of the genus. In 1840, in the first critical treatment of ''Tiarella'' since Linnaeus,

John Torrey John Torrey (August 15, 1796 – March 10, 1873) was an American botany, botanist, chemist, and physician. Throughout much of his career, he was a teacher of chemistry, often at multiple universities, while he also pursued botanical work, focus ...

and

Asa Gray Asa Gray (November 18, 1810 – January 30, 1888) is considered the most important American botanist of the 19th century. His ''Darwiniana'' was considered an important explanation of how religion and science were not necessarily mutually excl ...

described two new sections: * ''Tiarella'' sect. ''Anthonema'' : flowering stem leafy with alternate leaves; flowers

paniculate A panicle is a much-branched inflorescence. (softcover ). Some authors distinguish it from a compound spike inflorescence, by requiring that the flowers (and fruit) be pedicellate (having a single stem per flower). The branches of a panicle are of ...

; petals filiform or

subulate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

; western North America * ''Tiarella'' sect. ''Eutiarella'' : flowering stem naked; flowers racemose; petals oblong with a small claw or stalk; eastern North America. Olga Lakela highlighted the section names in 1937, but they have since fallen out of favor with botanists, mainly because ''Tiarella polyphylla'' is inconsistent with the dichotomy, but perhaps also because there are taxa with leafy flowering stems in both western and eastern North America. In Asia, the genus is represented by one species (''Tiarella polyphylla''). In North America, there have been numerous major treatments of genus ''Tiarella'', with taxonomies recognizing from two to six species, some including

infraspecific taxa In botany, an infraspecific name is the scientific name for any taxon below the rank of species, i.e. an infraspecific taxon or infraspecies. (A "taxon", plural "taxa", is a group of organisms to be given a particular name.) The scientific names ...

. Currently accepted taxonomies are based on three sources: # ''Tiarella polyphylla'' in ''Flora of China'' # ''Tiarella trifoliata'' and related taxa in ''

Flora of North America The ''Flora of North America North of Mexico'' (usually referred to as ''FNA'') is a multivolume work describing the native plants and naturalized plants of North America, including the United States, Canada, St. Pierre and Miquelon, and Greenla ...

'' # ''Tiarella cordifolia'' and related taxa in a paper published by

in 2021 The treatment in the first source is near-universally accepted, the second is widely recognized, while the third is new and growing in acceptance. A few authorities (with global scope) accept all three.

Infrageneric taxa

All names used in this section are taken from the International Plant Names Index, except where noted. The geographical locations are taken from

Plants of the World Online Plants of the World Online (POWO) is an online database published by the Royal Botanic Gardens, Kew. It was launched in March 2017 with the ultimate aim being "to enable users to access information on all the world's known seed-bearing plants by ...

(POWO). , POWO accepts 7 species and 3 infraspecies: * ''

Tiarella austrina ''Tiarella austrina'' is a species of flowering plant in the family Saxifragaceae. The specific name ''austrina'' means "from the south". Being endemic to the southeastern United States, it is sometimes referred to as the southern foamflower. It ...

'' : Alabama, Georgia, North Carolina, South Carolina, Tennessee * ''

Tiarella cordifolia ''Tiarella cordifolia'', the heart-leaved foamflower, is a species of flowering plant in the family Saxifragaceae. The specific name ''cordifolia'' means "with heart-shaped leaves", a characteristic shared by all taxa of ''Tiarella'' in eastern N ...

sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

: Georgia, Maryland, North Carolina, South Carolina, Virginia * ''

Tiarella nautila ''Tiarella nautila'' is a species of flowering plant in the family Saxifragaceae. The specific name ''nautila'' alludes to its sail-like stem leaves. Accordingly, it is sometimes called the sail-leaf foamflower. The species is narrowly endemic to ...

'' : Georgia, North Carolina, Tennessee * ''

Tiarella polyphylla ''Tiarella polyphylla'' is a species of flowering plant in the family Saxifragaceae. The specific name ''polyphylla'' means "many-leaved". The species is native to Asia, ranging from the eastern Himalayas to China, east Asia, and southeast Asia. ...

'' : Assam, China, East Himalaya, Japan, Korea, Myanmar, Nepal, Taiwan, Tibet * ''

Tiarella stolonifera ''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'', whi ...

'' : Connecticut, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Brunswick, New Hampshire, New Jersey, New York, North Carolina, Nova Scotia, Ohio, Ontario, Pennsylvania, Québec, Rhode Island, Tennessee, Vermont, Virginia, West Virginia, Wisconsin * ''

Tiarella trifoliata ''Tiarella trifoliata'', the three-leaf foamflower, is a species of flowering plant in the family (biology), family Saxifragaceae. The specific name ''trifoliata'' means "having three leaflets", a characteristic of two of the three recognized var ...

'' ** ''Tiarella trifoliata'' var. ''laciniata'' : British Columbia, Oregon, Washington ** ''Tiarella trifoliata'' var. ''trifoliata'': Alaska, Alberta, British Columbia, California, Idaho, Montana, Oregon, Washington ** ''Tiarella trifoliata'' var. ''unifoliata'' : Alaska, Alberta, British Columbia, California, Idaho, Montana, Oregon, Washington * ''

Tiarella wherryi ''Tiarella wherryi'' is a species of flowering plant in the family Saxifragaceae. The specific name ''wherryi'' recognizes Edgar Wherry, the botanist who collected some of the first specimens in the early 1930s. Commonly called Wherry's foamflow ...

'' : Alabama, Georgia, Kentucky, Mississippi, Tennessee

Distribution

''Tiarella'' is native to Asia and North America. It has been introduced into Norway.

Asia

'' is an Asian species, ranging from the eastern Himalayas to China, east Asia, and southeast Asia. In China, it is found in moist forests and shady wet places at altitudes from .

Western North America

In western North America, ''

'' ranges from California northward to Alaska, and eastward to Montana. Within this region, the varieties of ''T. trifoliata'' have overlapping ranges. Canada: * ''Alberta'': , * ''British Columbia'': , , United States: * ''Alaska'': , * ''California'': , * ''Idaho'': , * ''Montana'': , * ''Oregon'': , , * ''Washington'': , ,

Eastern North America

In eastern North America, ''Tiarella cordifolia'' sensu lato is wide ranging, from northeastern Wisconsin across southeastern Canada to Nova Scotia, extending southward through the Appalachians into Alabama and Mississippi. The range of ''Tiarella cordifolia''

is narrowly confined to the

East Coast of the United States The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The eastern seaboard contains the coa ...

from Maryland through Virginia and the Carolinas into Georgia. At least one species of ''Tiarella'' occurs in each of 26 provinces and states. Multiple species of ''Tiarella'' occur in eight (8) states. ''

'' occurs in 22 provinces and states, it being the only species of ''Tiarella'' in 17 of those provinces and states. ''

'' sensu stricto occurs in just five (5) states, all of which have at least two ''Tiarella'' species. The ranges of ''

'', ''

'', and ''

'' overlap in Tennessee, North Carolina, and Georgia. Canada: * ''New Brunswick'': ''T. stolonifera'' * ''Nova Scotia'': ''T. stolonifera'' * ''Ontario'': ''T. stolonifera'' * ''Québec'': ''T. stolonifera'' United States: * ''Alabama'': ''T. austrina'', ''T. wherryi'' * ''Connecticut'': ''T. stolonifera'' * ''Georgia'': ''T. austrina'', ''T. cordifolia'', ''T. nautila'', ''T. wherryi'' * ''Kentucky'': ''T. stolonifera'', ''T. wherryi'' * ''Maine'': ''T. stolonifera'' * ''Maryland'': ''T. cordifolia'', ''T. stolonifera'' * ''Massachusetts'': ''T. stolonifera'' * ''Michigan'': ''T. stolonifera'' * ''Mississippi'': ''T. wherryi'' * ''New Hampshire'': ''T. stolonifera'' * ''New Jersey'': ''T. stolonifera'' * ''New York'': ''T. stolonifera'' * ''North Carolina'': ''T. austrina'', ''T. cordifolia'', ''T. nautila'', ''T. stolonifera'' * ''Ohio'': ''T. stolonifera'' * ''Pennsylvania'': ''T. stolonifera'' * ''Rhode Island'': ''T. stolonifera'' * ''South Carolina'': ''T. austrina'', ''T. cordifolia'' * ''Tennessee'': ''T. austrina'', ''T. nautila'', ''T. stolonifera'', ''T. wherryi'' * ''Vermont'': ''T. stolonifera'' * ''Virginia'': ''T. cordifolia'', ''T. stolonifera'' * ''West Virginia'': ''T. stolonifera'' * ''Wisconsin'': ''T. stolonifera'' A disjunct population of ''Tiarella'' occurs in Stearns County, Minnesota but botanists believe it was introduced. That population is claimed to be ''T. stolonifera'', but evidence is lacking.

Conservation

In western North America, ''Tiarella trifoliata'' is globally secure (G5). Each variety is globally secure as well. In eastern North America, ''Tiarella cordifolia'' sensu lato is globally secure (G5). It is frequent to common throughout most of its wide distribution but becomes rare at the edges of its range, in Wisconsin and the western Upper Peninsula of Michigan, Nova Scotia, New Jersey, and Mississippi.

Cultivation

Many hybrids are known and cultivated. The following have been given the Royal Horticultural Society's

Award of Garden Merit The Award of Garden Merit (AGM) is a long-established annual award for plants by the British Royal Horticultural Society (RHS). It is based on assessment of the plants' performance under UK growing conditions. History The Award of Garden Merit ...

: *''Tiarella'' = 'Gowing' *''Tiarella'' 'Spring Symphony' *''Tiarella cordifolia'' *''Tiarella wherryi'' File:Foamflower Tiarella 'Cygnet' Flower Closeup 2000px.JPG, ''Tiarella'' 'Cygnet' flowers File:Foamflower Tiarella 'Cygnet' Leaves 2054px.jpg, ''Tiarella'' 'Cygnet' leaves

References

Bibliography

* * * * * * *

External links

* * * * * * * * * Saxifragaceae Saxifragaceae genera Groundcovers {{Saxifragaceae-stub