Saxifraga


Saxifraga is the largest genus in the family Saxifragaceae, containing about 440 species of holarctic perennial plants, known as saxifrages or rockfoils. The Latin word saxifraga means literally "stone-breaker", from Latin :wikt:saxum + :wikt:frangere. It is usually thought to indicate a medicinal use for treatment of urinary calculi, rather than breaking rocks apart.

Description

Most saxifrages are small perennial, biennial or annual 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.
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. and it lives in tundral ecosystems.

Taxonomy

A genus of about 440 species. The former monotypic genus Saxifragella has been submersed within Saxifraga, the largest genus in Saxifragaceae, as Saxifraga bicuspidata. Also the genus Saxifragopsis was previously included in Saxifraga.

Subdivision

Based on morphological criteria, up to 15 sections were recognised. 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. Modern floras separate these groups as the genus Micranthes.
The thirteen sections are;
Plants formerly placed in Saxifraga are mainly but not exclusively Saxifragaceae. They include:
Several plant genera have names referring to saxifrages, although they might not be close relatives of Saxifraga. They include:
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:
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 above sea level in the Alps, or the East Greenland saxifrage. 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 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.
Charles Darwin – erroneously believing Saxifraga to be allied to the sundew family – suspected the sticky-leaved round-leaved saxifrage, rue-leaved saxifrage and Pyrenean saxifrage to be protocarnivorous plants, and conducted some experiments whose results supported his observations, but the matter has apparently not been studied since his time.

Cultivation

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.
S. × urbium, a hybrid between Pyrenean saxifrage and St. Patrick's cabbage, is commonly grown as an ornamental plant. Another horticultural hybrid is Robertsoniana saxifrage, derived from kidney saxifrage and Pyrenean saxifrage. Some wild species are also used in gardening. Cambridge University Botanic Garden hosts the United Kingdom's national collection of saxifrages.

Award of Garden Merit

The following species and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-
Purple saxifrage is a popular floral emblem. It is the territorial flower of Nunavut and the county flower of County Londonderry in Northern Ireland. Known as rødsildre in Norway, it also is the county flower of Nordland. It is on the seal of Fitchburg State University, whose motto is "Perseverantia" in reference to the rock-breaking abilities of the plant over time. Tsukuba in Japan has as its city flower hoshizaki-yukinoshita, the aptera form of Creeping saxifrage. The leaves of the Japanese variety "yukinoshita" can also been eaten, and is consumed at least within the large southern island of Kyushu. It is prepared by frying the younger succulent leaves in tempura batter. The leaves of Saxifraga pensylvanica can also be eaten raw or cooked.