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.
The habitat of this plant is northern seashores and sea shingle. The habit is prostrate, then ascending. The root-stock is fleshy, and the plant is stoloniferous. The stems are leafy, much-branched. The plant is hairless, bluish-green. The leaves are fleshy, egg-shaped, acute, rough, with hard dots, in 2 rows, the lower stalked, the upper stalkless, with prominent horny points (when dry), and are said to taste like oysters. The flowers are purplish-blue and pink, in forked cymes, with 2 opposite, leafy bracts below. The flower-stalks are short, curved back in fruit. The calyx in fruit is angular. The corolla is 5-lobed to the middle, with yellow folds or protuberances in the throat. The nutlets are flattened, large, fleshy, free, smooth, and form a pyramid, the membranous outer coat becoming inflated and papery, rounded on the back, and longer than the calyx. The seed-cavity is larger than the seeds. The plant is 1-2 ft. high, flowering between May and August, and is a herbaceous perennial.