Saxifraga is the largest genus in the family Saxifragaceae, containing about 473 species of holarctic perennial plants, known as saxifrages[1][2] or rockfoils.[3] The Latin word saxifraga means literally "stone-breaker", from Latin saxum ("rock" or "stone") + frangere ("to break"). It is usually thought to indicate a medicinal use for treatment of urinary calculi (known as kidney or bladder stones), rather than breaking rocks apart.[2][4]
Description
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Most saxifrages are small perennial, biennial (e.g. S. adscendens) or annual (e.g. S. tridactylites) herbaceous plants whose basal or cauline leaves grow close to the ground, often in a rosette. The leaves typically have a more or less incised margin; they may be succulent, needle-like and/or hairy, reducing evaporation.[5][6][7]
The inflorescence or single flower clusters rise above the main plant body on naked stalks. The small actinomorphic hermaphrodite flowers have five petals and sepals and are usually white, but red to yellow in some species. Stamens, usually 10, rarely 8, insert at the junction of the floral tube and ovary wall, with filaments subulate or clavate. As in other primitive eudicots, some of the 5 or 10 stamens may appear petal-like.[citation needed] and it lives in tundral ecosystems.[5][8][6]
Taxonomy
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A genus of about 473 species.[1] The former monotypic genus Saxifragella has been submersed within Saxifraga, the largest genus in Saxifragaceae, as Saxifraga bicuspidata.[9][5] Also the genus Saxifragopsis (strawberry saxifrage) was previously included in Saxifraga.[10]
Subdivision
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Based on morphological criteria, up to 15 sections were recognised.[11] Subsequent molecular phylogenetic studies reduced this to 13 sections with 9 subsections. The former sections Micranthes and Merkianae are more closely related to the Boykinia and Heuchera clades.[12] Modern floras separate these groups as the genus Micranthes.[13][6]
Saxifraga × urbium – London pride (S. spathularis × S. umbrosa)
Saxifraga umbrosa – Pyrenean saxifrage
Saxifraga vandelli
Saxifraga wahlenbergii
Formerly placed here
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Plants formerly placed in Saxifraga are mainly but not exclusively Saxifragaceae. They include:[citation needed]
Astilboides tabularis, as S. tabularis
Bergenia crassifolia, as S. cordifolia, S. crassifolia
Bergenia pacumbis, as S. ligulata, S. pacumbis
Bergenia purpurascens, as S. delavayi, S. purpurascens
Boykinia jamesii, as S. jamesii
Boykinia occidentalis (Coastal Brookfoam), as S. elata
Boykinia richardsonii (Richardson's Brookfoam), as S. richardsonii
Darmera peltata (Indian Rhubarb), as S. peltata
Leptarrhena pyrolifolia, as S. pyrolifolia
Luetkea pectinata (Partridgefoot), as S. pectinata
Micranthes, including:
Micranthes integrifolia (wholeleaf saxifrage)
Micranthes howellii (Howell's saxifrage),[15] as S. howellii
Micranthes stellaris (Starry saxifrage),[15] as S. stellaris
Mukdenia rossii (Mukdenia), as S. rossii
Other "saxifragous" plants
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Several plant genera have names referring to saxifrages, although they might not be close relatives of Saxifraga. They include:[citation needed]
Golden-saxifrages, Chrysosplenium
Burnet-saxifrages, Pimpinella
Pepper-saxifrage, Silaum silaus. The name "silaum" comes from the Latin word sil, which means yellow ochre. This refers to the sulphurous yellow colour of the flowers.[17]
Some plants refer to Saxifraga in their generic names or specific epithets, either because they are also "rock-breaking" or because they resemble members of the saxifrage genus:[citation needed]
Campanula saxifraga
Celmisia saxifraga (Benth.) W.M.Curtis
Cineraria saxifraga DC.
Dryopteris saxifraga
Petrorhagia saxifraga – Tunicflower
Pimpinella saxifraga – Burnet saxifrage
Ptychotis saxifraga
Saxifragella
Saxifragodes
Saxifragopsis Small
Ecology
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Round-leaved saxifrage (S. rotundifolia), whose sticky leaves seem to catch small invertebrates
Saxifrages are typical inhabitants of Arctic–alpine ecosystems, and are hardly ever found outside the temperate parts of the Northern Hemisphere; most members of this genus are found in subarctic climates. A good number of species grow in glacial habitats, such as S. biflora which can be found some 4,000 m (13,000 ft) above sea level in the Alps, or the East Greenland saxifrage (S. nathorstii). The genus is also abundant in the Eastern and Western Himalayan alpine shrub and meadows. Though the archetypal saxifrage is a small plant huddling between rocks high up on a mountain, many species do not occur in such a habitat and are larger (though still rather delicate) plants found on wet meadows.
Various Saxifraga species are used as food plants by the caterpillars of some butterflies and moths, such as the Phoebus Apollo (Parnassius phoebus).[18]
Charles Darwin – erroneously believing Saxifraga to be allied to the sundew family (Droseraceae) – suspected the sticky-leaved round-leaved saxifrage (S. rotundifolia), rue-leaved saxifrage (S. tridactylites) and Pyrenean saxifrage (S. umbrosa) to be protocarnivorous plants, and conducted some experiments whose results supported his observations,[19] but the matter has apparently not been studied since his time.
Cultivation
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Saxifraga urumoffii at the Royal Botanic Garden Edinburgh.
Numerous species and cultivars of saxifrage are cultivated as ornamental garden plants, valued particularly as groundcover or as cushion plants in rock gardens and alpine gardens. Many require alkaline or neutral soil to thrive.[7]
S. × urbium (London pride), a hybrid between Pyrenean saxifrage (S. umbrosa) and St. Patrick's cabbage (S. spathularis), is commonly grown as an ornamental plant.[2] Another horticultural hybrid is Robertsoniana saxifrage (S. × geum), derived from kidney saxifrage (S. hirsuta) and Pyrenean saxifrage.[citation needed] Some wild species are also used in gardening. Cambridge University Botanic Garden hosts the United Kingdom's national collection of saxifrages.[2]
Award of Garden Merit
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The following species and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-[20]
The leaves of some saxifrage species, such as creeping saxifrage (S. stolonifera) and S. pensylvanica,[51] are edible. The former is a food in Korea[52] and Japan.[citation needed] The flowers of purple saxifrage (S. oppositifolia) are eaten in Nunavut, Canada and the leaves and stems brewed as a tea.[53]
Species are also used in traditional medicine, such as creeping saxifrage in East Asia[54] and round-leaved saxifrage (S. rotundifolia) in Europe.[55]
Two species—purple saxifrage and creeping saxifrage—are popular floral emblems. They are official flowers for:
^ abcdefghijklmnopqrstuvwxUmberto Quattrocchi. CRC World Dictionary of Plant Names: Common Names, Scientific Names, Eponyms. Synonyms, and Etymology. CRC Press, 1999. p.2395-2396. ISBN 9780849326738
^Knaben, G. (1934). "Saxifraga osloensis n. sp., a tetraploid species of the Tridactylites section". Nytt Magasin for Botanikk: 117–138.
^Reader's Digest Nature Lover's Library Wild Flowers of Britain, page 192, published 1988
^Ivo Novák (1980). A Field Guide in Colour to Butterflies and Moths. Octopus Books. ISBN 0-7064-1293-1.
^Charles Darwin (1875). "Drosophyllum – Roridula – Byblis – glandular hairs of other plants – concluding remarks on the Droseraceae". Insectivorous Plants (1st ed.). London: J. Murray. pp. 332–367.
^"AGM Plants - Ornamental"(PDF). Royal Horticultural Society. July 2017. p. 95. Retrieved 1 November 2018.
^Niering, William A.; Olmstead, Nancy C. (1985) [1979]. The Audubon Society Field Guide to North American Wildflowers, Eastern Region. Knopf. p. 780. ISBN 0-394-50432-1.
^Ji-xian Guo, Ki Sung Chung, Paul Pui-hay But, Takeatsu Kimura (1996). International Collation Of Traditional And Folk Medicine, Vol 2: Northeast Asia Part 2. World Scientific Publishing Company. p. 65.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Pieroni, Andrea; Quave, Cassandra L., eds. (2014). Ethnobotany and Biocultural Diversities in the Balkans. New York: Springer.
Gornall, Richard J. (December 1987). "An outline of a revised classification of Saxifraga L.". Botanical Journal of the Linnean Society. 95 (4): 273–292. doi:10.1111/j.1095-8339.1987.tb01860.x.
Soltis, Douglas E.; Kuzoff, Robert K.; Conti, Elena; Gornall, Richard; Ferguson, Keith (March 1996). "matK and rbcL Gene Sequence Data Indicate that Saxifraga (Saxifragaceae) is Polyphyletic". American Journal of Botany. 83 (3): 371. doi:10.2307/2446171. JSTOR 2446171.