Saxifraga aizoides L., Yellow Saxifrage
Account Summary
Native, very rare. European arctic-montane, also in N America and Greenland.
1902; Abraham, J.T. & McCullagh, F.; western end, Cliffs of Magho.
April to October.
Growth form, recognition and preferred habitats
A loose cushion- or thick mat-forming perennial with medium to dark green, very fleshy, linear to oblong, stalkless and nerveless, apiculate leaves that are very variable in length. The leaf margin is usually, but not always, furnished with stout, forwardly directed tooth-like hairs. One to three hydathode glands (sometimes referred to as 'chalk glands') near the leaf-tip may or may not secrete lime, so that calcareous incrustation is often slight or absent. From June to September, some of the stems terminate in an erect flowering portion, 7-20 cm tall, bearing a short, leafy cyme of 2-15 flowers. The petals are usually yellow (often bearing orange spots), but less commonly the flowers can range from pale yellow to orange or even brick red (Thompson 1911; Webb & Gornall 1989).
S. aizoides is most often found on the banks of mountain streams, or where water continuously seeps across rocky ledges, screes, or surfaces with crevices, or wet, grassy slopes. In addition to its requirement for a constant water supply, this fleshy, almost succulent-leaved saxifrage is also a marked calcicole in its nutrient demands: basic rock, or base-rich flushing water is always present wherever it occurs. Webb & Gornall (1989) describe this as a "calcicole tendency", as in their wider experience of the species, they find it will tolerate "any except very base-poor habitats".
Irish occurrence
A rare arctic-alpine plant in Ireland, elsewhere apart from its one Fermanagh station, this perennial occurs about Donegal Bay (mainly in Cos Sligo and Leitrim (H28, H29)), plus at one site in NE Antrim (H39) (New Atlas).
Fermanagh occurrence
In Fermanagh, S. aizoides occurs in considerable numbers over an area of cliff covered by three tetrads (or four 1-km squares), along the north-facing Cliffs of Magho (otherwise known as Poulaphouca), that overlook Lower Lough Erne. It is always found growing in very wet, unstable parts of the cliff where the rock face is eroded and in many, but not all, parts of this linear station, it is shaded by wet upland mixed deciduous oak-birch-ash woodland.
Lusby et al. (1996) describe the species habitat in Scotland, where the species has its B & I headquarters very accurately, as being, "on the banks of mountain streams, on flushed grassy slopes or on rocky banks or cliff faces where there is a constant seepage of water". Flushed or dripping rocky banks, cliff ledges and wet screes at the base of the cliff, precisely describes the Fermanagh habitats of this plant.
Associated species
In B & I, S. aizoides is frequently associated with other interesting arctic-alpines such as Saxifraga oppositifolia (Purple Saxifrage), Silene acaulis (Moss Campion) and Thalictrum alpinum (Alpine Meadow-rue), none of which have ever been found in Fermanagh (Raven & Walters 1956). While Dryas octopetala (Mountain Avens) has been recorded from the same Fermanagh cliffs over 90 years ago, the currently associated species of interest include only Listera ovata (Common Twayblade), Parnassia palustris (Grass-of-Parnassus), Pinguicula vulgaris (Common Butterwort), Primula vulgaris (Primrose) and Sesleria caerulea (Blue Moor-grass).
S. aizoides forms loose, spreading cushions by means of creeping decumbent sterile stems and it is easy to imagine seed from the profuse flowers on separate, erect fertile stems being readily transported to lower altitudes by the flowing water that soaks the plants (McCallum Webster 1978). Seed of the species is also said to be transported by birds (Lusby et al. 1996), but this is hard to imagine in the particular wet, wooded Fermanagh station occupied. In NI, S. aizoides is a protected species under Schedule 8 of the Wildlife (NI) Order 1985.
British occurrence
S. aizoides is common and widespread in N & W Scotland from sand-dunes at sea level to 1175 m on the mountains of Mid-Perthshire (Pearman et al. 2008). On account of its connection with flushing water, in Scotland plants and seeds are often washed downstream and can become established on river shingle and by the sides of streams (McCallum Webster 1978).
Yellow Saxifrage also features on the mountains of Cumbria and the N Yorkshire Pennines, which represent the southern limit of the species' northern Europe distribution (Webb & Gornall 1989; New Atlas).
European and world occurrence
In mainland Europe, the distribution of S. aizoides fits the classical arctic-alpine pattern. It stretches from Iceland and Spitsbergen to N & W Scandinavia, and locally to NW Russia. It has two stations in the French Jura and is common throughout the Alps and frequent in the Pyrenees and Carpathians. From the Alps, it extends southwards to the C Apennines and through the mountains of the Balkans to NW Macedonia (Webb & Gornall 1989, Map 39; Jalas et al. 1999, Map 3161).
Beyond Europe, it is found in Greenland and is widespread in arctic and subarctic Canada, with southward extensions near the E & W coasts of N America. In Asia, it is found only in Novaya Zemlya and the polar Urals (Webb & Gornall 1989, Map 38; Hultén & Fries 1986, Map 1024).
Threats
None.