This section is from the book "British Wild Flowers In The Four Seasons", by Thomas Moore. Also available from Amazon: British Wild Flowers.
* Leaves opposite, densely crowded.
S. oppositifolia: stems creeping; leaves small, opposite, obovate, overlapping, fringed; flowers large, purple, solitary, on short erect branches, but so numerous as to cover the stems. - Alpine rocks. Fl. April.
** Leaves alternate, the upper ones distant.
S. granulata: stem erect, hairy; lower leaves reniform, bluntly crenate; flowers largish, white, in terminal cymes. - Meadows and pastures. Fl. May.
S. tridactylites: annual; stem short, erect, usually red; leaves small, entire or three-lobed; flowers small, white. - Walls and dry barren places. Fl. April, May.
 
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