''Tiarella'', the foamflowers, is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Saxifragaceae Saxifragaceae is a family of Herbaceous plant, herbaceous Perennial plant, perennial flowering plants, within the core eudicot Order (biology), order Saxifragales. The Taxonomy (biology), taxonomy of the family has been greatly revised and the ...

. 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 In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...

herbaceous plant Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...

s with short, slender

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

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

stolon In biology, a stolon ( from Latin ''wikt:stolo, stolō'', genitive ''stolōnis'' – "branch"), also known as a runner, is a horizontal connection between parts of an organism. It may be part of the organism, or of its skeleton. Typically, animal ...

s; 2) size and shape of basal leaves; and 3) presence or absence of stem leaves (also called cauline leaves). 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 The Blue Ridge Mountains are a Physiographic regions of the United States, physiographic province of the larger Appalachian Highlands range. The mountain range is located in the Eastern United States and extends 550 miles southwest from southern ...

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 in 2021:

Taxonomy

In 1753, Swedish botanist

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

established

''Tiarella'' by recognizing two

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, ''Tiarella cordifolia'' and ''Tiarella trifoliata''. A third species, ''Tiarella polyphylla'', was described by

David Don David Don (21 December 1799 – 15 December 1841) was a Scottish botanist. Biography David Don was born on 21 December 1799 at Doo Hillock, Forfar, Angus, Scotland to Caroline Clementina Stuart, and her husband George Don of Forfar. His olde ...

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 botany, botanist of the 19th century. His ''Darwiniana'' (1876) was considered an important explanation of how religion and science were not necessaril ...

described two new sections: * ''Tiarella'' sect. ''Anthonema'' : flowering stem leafy with alternate leaves; flowers paniculate; petals filiform or subulate; western North America * ''Tiarella'' sect. ''Eutiarella'' : flowering stem naked; flowers

racemose A raceme () or racemoid is an unbranched, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are produced as the shoo ...

; 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. 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 Guy Nesom 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 The International Plant Names Index (IPNI) describes itself as "a database of the names and associated basic bibliographical details of seed plants, ferns and lycophytes." Coverage of plant names is best at the rank of species and genus. It inclu ...

, except where noted. The geographical locations are taken from

Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

(POWO). , POWO accepts 7 species and 3 infraspecies: * '' Tiarella austrina'' : Alabama, Georgia, North Carolina, South Carolina, Tennessee * '' Tiarella cordifolia''

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 c ...

: Georgia, Maryland, North Carolina, South Carolina, Virginia * '' Tiarella nautila'' : 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'' : 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'' 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'' : Alabama, Georgia, Kentucky, Mississippi, Tennessee

Distribution

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

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

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, '' Tiarella trifoliata'' 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 ''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 ...

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 region encompassing the coast, coastline where the Eastern United States meets the Atlantic Ocean; it has always pla ...

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. '' Tiarella stolonifera'' occurs in 22 provinces and states, it being the only species of ''Tiarella'' in 17 of those provinces and states. '' Tiarella cordifolia'' sensu stricto occurs in just five (5) states, all of which have at least two ''Tiarella'' species. The ranges of '' Tiarella nautila'', '' Tiarella wherryi'', and '' Tiarella austrina'' 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 Stearns County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 158,292. Its county seat and largest city is St. Cloud. Included within the Minnesota Territory since 1849, the county was founded by Europe ...

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 The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr ...

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

: *''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

* * * * * * * * * * * {{Taxonbar, from=Q1456298 Saxifragaceae Saxifragaceae genera Groundcovers Taxa named by Carl Linnaeus