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.
St. John's Wort (Hypericum undulatum, Schousb.). - The habitat of this plant is bogs. The habit is erect. The stem is slender, branched, 4-edged. The leaves are oblong, wavy at the edge (hence undulatum), bent down, with numerous transparent dots, netted with transparent veins (as are the stem edges and sepals), with black dots on the margins below, the dots numerous and uniform. The flowers are yellow, in loose, much-branched cymes. The sepals are erect, egg-shaped to lance-shaped, acute, with blunt scallops, glandular, with a long, fine point. The petals are narrow, tinged on the outside on one longitudinal half with red. The anthers have a black spot. The styles are half as long as the sepals, spreading, not half as long as the capsule. The carpels have many vittae. The plant is 2-3 ft. high, flowering in July and August, and is a herbaceous perennial.
Bog St. John's Wort (Hypericum elodes, L.). - The habitat of this plant is spongy bogs, wet moors, and ditches. The habit is ascending or creeping. The plant is shaggy, rooting below. The stems are round, creeping, numerous, prostrate below, then ascending, leafy. The leaves are round to egg-shaped, or oblong to heart-shaped, stalkless, shaggy, half-clasping, with small pellucid to dotted glands. The flowers are pale-yellow, in few-flowered terminal and axillary cymes, irregular, divided into 3 repeatedly. The bracts are small, triangular, with glands at the teeth. The sepals are nearly equal, hairless, oblong, blunt, fringed, short-stalked, with reddish glands. The petals are equal-sided, egg-shaped, entire. The styles are 3, and nearly as long as the capsule. The stamens are in three sets, with a scale between, united in the lower half. The plant is 3-12 in. high, flowering in July and August, and is a herbaceous perennial.