This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Small-seeded as it is there is nothing to prevent its occurrence in Glacial beds, but the minuteness of the seeds would seem to prevent their detection. The Northern Temperate Zone of Europe, N. Africa, N. and W. Asia, is the region in which this little plant is found. In Great Britain it is present throughout the Peninsula, Channel, Thames, Anglia, and Severn provinces; but not in Radnor or Cardigan in S. Wales, Montgomery, or in N. Wales; in the Trent province; not in Mid Lancs in the Mersey province; generally in the Humber and Tyne provinces; not in the Isle of Man; in the Lakes province; and only in Haddington, Edinburgh, and Linlithgow in the East Low-lands; in Fife, W. and Mid Perth, Forfar, Aberdeen, in the E. Highlands, and in Easterness, N. Ebudes, E. Ross, E. Sutherland, and Caithness; elsewhere from E. Scotland, that is from Caithness, to Cornwall and Kent, it is otherwise general. It is found in Yorkshire at 1800 ft. It is native in Ireland and the Channel Islands. The Rue-leaved Saxifrage is a familiar wall plant, growing abundantly on the tops of mud walls or on rocks, rarely on the ground, with Whitlow Grass, and Stonecrop of various kinds. Thale Cress is similarly addicted to this same type of habitat.
This pretty little Saxifrage, so familiar on wall tops, is an erect plant, with usually a reddish single-branched stem, and with leaves wedge-shaped, 3-5-lobed or divided, alternate. The stem-leaves are covered, like many other xerophytes, with absorbent, stalked, sticky glands, which capture insects. The plant may be insectivorous. The lower leaves are entire and spoon-shaped.
Photo. Flatters & Garnett - Rue-leaved Saxifrage (Saxifraga tridactylites, L.)
The single white flowers are borne on flower-stalks, with 2 bracts at the base, and longer than the fruit. The petals are only slightly longer than the calyx. The capsule is 2-chambered, with numerous, minute, blackish-brown seeds.
This plant is about 3-6 in. in height. The flowers follow on after Whitlow Grass, from April till July. Rue-leaved Saxifrage is annual.
The flowers yield honey and are proterandrous. The stamens move singly in succession towards the centre of the flower, which, however, is proterogynous, the stigma ripening first. The male flowers are larger and more conspicuous than the female. The anthers ripen one after another and bend inwards towards the centre. After they open they bend out again and cross-pollinate the flower. It is visited by bees, flies, and beetles.
The capsule is many-seeded and opens above, and having short spreading beaks the seeds are scattered around, being aided by the wind which sways the rigid stems, or by being touched by passing animals.
Rue-leaved Saxifrage is a sand-loving plant loving sand soil, but will also grow on lime found in the mortar of walls, calcareous rocks, and elsewhere.
The only fungus that infests it is Puccinia saxifraga, one of the cluster-cups.
No insects feed upon it.
Saxifraga, Pliny, is from the Latin saxum, stone, frango, break, meaning stone-breaker; and the second Latin name means three-fingered in Greek, alluding to the trifid lobes of the upper leaves.
The plant is called Whitlow Grass, Nailwort, White Blow. Gerarde uses the first name in allusion to a supposed property it had of healing disease of the nails called Whitlow, and the same reason explains the second name. The Saxifrage was said to reveal witches.
Essential Specific Characters: 109. Saxifraga tridactylites, L. - Stem leafy, branched, leaves cuneate, trifid, flowers small, white, terminal on a separate stalk, with 2 bracts below.