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.
This plant is rare and not indigenous, being found in hedges, on old walls near gardens, former religious houses, ruins, and waste places. The habit is creeping, then erect. The rootstock is woody. The plant is devoid of hairs. The stems are erect, simple, numerous, angled. The leaves are broadly heart-shaped, blunt, with a short point, netted, smooth, bluish - green beneath, with rounded auricles, incurved, and nearly overlapping. The flowers are 4-8, in a cluster, pale-yellow, on very short stalks, more or less erect. The calyx is yellow, with a slender curved tube, rounded below. The lip is oblong or ovate, the throat swollen. The corolla is pear-shaped. The flower-stalks are bent-down. The fruit is a 6-valved capsule, the seeds nearly round, flattened, granulated, excavated on the ventral face. The plant is 1-2 ft. high, flowering in July and August, and is a herbaceous perennial.