Saxifraga tridactylites is a small native plant, ‘scarce’ in Scotland but widespread in England. It’s a winter annual, meaning its seeds germinate in the autumn, the seedlings survive the winter, and then by spring they are ready to develop rapidly, flower and produce seed. Most of our early-flowering annuals are ‘winter annuals’.
Saxifraga tridactylites, Aberlady Bay, East Lothian. Photo: Chris Jeffree.
The first record of this species ever made in the British Isles is believed to have been by the herbalist John Gerard in 1597. He described the habitat thus:
“upon bricke and stone wals, upon olde tiled houses, which are growen much moss on them..upon the brike wall in Chancerie Lane belonging to the Earl of Southampton in the suburbs of London”.
Gerard’s ‘snapshot’ of habitat fits the modern description from the BSBI:
“dry, open habitats such as sandy grassland, limestone pavement and rock ledges, cliffs and screes, and on man-made structures like mortared walls, pavements and railway tracks. It is most commonly found on base-rich substrates, often on skeletal soils or virtually bare rock”.
Its leaves are fleshy, and the lower ones are usually lobed (3-5 lobes). It has white flowers with 5 petals, each only 2-3 mm. The flowers are grouped upon stiffish stems, a few cm in length. The whole plant is usually red.
Saxifraga tridactylites from Gullane (East Lothian) and Stevenston (Ayrshire). Photos: Chris Jeffree.
In our exploration of Scotland’s urban flora we have found it a few times in human-dominated settings. At the small town of Annan in May 2019 (Dumfries and Galloway) it was growing en masse in a builder’s yard (see the image below). A month ago we found it in Stevenston (North Ayrshire) where it was growing on a decrepit road surface at the entrance to the Ardeer industrial site.
A typical urban habitat of Saxifraga tridactylites. We were excited to find the plants in a builder’s yard at Annan (Dumfries and Galloway). There were several hundred plants growing together. Photo: John Grace.
Almost everyone likes saxifrages, and rock-gardening enthusiasts collect them for their beauty. This one is a miniature. It isn’t generally grown in rock-gardens and it is not available online from horticultural suppliers. But some people have complained about this particular saxifrage: in North America it may be invasive and I found the following comment:
“..it has rapidly naturalized in two geographically distinct areas of the United States: the Southeast and the Northwest. In the Southeast, the spread has been exceedingly fast and poses a potential threat to xeric limestone habitats of the Interior Low Plateau and Ridge and Valley physiographic provinces”
If we look at the BSBI’s distribution map (below), we can see immediately that the species has spread in Ireland and in the Central Belt of Scotland. Its very recent spread in the Glasgow area suggests a new and more aggressive genetic strain might have arisen in the last few years. The species isn’t even mentioned in older books on the flora of Glasgow (Lee 1933, Dixon 2000). I am sure there is an evolutionary process at work in human-dominated landscapes. Streets are annually drenched with herbicides and the thin layers of soil are ‘fertilised’ by the excreta of dogs. There must be strong selection pressures favouring short life cycles and chemically resistant cuticles. Urban ecotypes are not however generally recognised by the scientific community. It is time for some new research on the genetics of urban species !
In fact, the topic has attracted some limited attention – one publication in the journal Conservation Genetics raises the specific question of how Saxifraga tridactylites has extended its distribution range in the man-made landscape of central Europe (Reisch 2009).
The distribution of Saxifraga tridactylites before 2000 (left) and the present map showing all records, colour coded, to spring 2022. The 2022 records are shown as green. Notable new appearances have been in Ireland and in the Central Belt of Scotland.
As for its name, saxifrage is from the Latin and means ‘stone-breaker’, referring to its medicinal use to treat gall stones (it doesn’t break rocks!). The specific name tridactylites comes from the Greek, daktylos, ‘a finger’ and ‘tri-‘ refers to the three ‘fingers’ or lobes of the lower leaves. It’s called the ‘Rue-leaved’ saxifrage because the tri-lobed leaves look a bit like those of Rue Ruta graveolens.
References
Dixon JH et al. (2000) The Changing Flora of Glasgow. Edinburgh University Press.
Lee JR (1933) The Flora of the Clyde Area. John Smith, Glasgow.
Reisch C (2009) Genetic structure of Saxifraga tridactylites (Saxifragaceae)
from natural and man-made habitats. Conservation Genetics 8, 893-903.
©John Grace
Botany in Scotland 
It is quite common on the limestone plateau called Alvaret on the Swedish island Öland in the Baltic.
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Thank you Kerstein, that’s very good to know. John
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