This section is from the book "Wayside And Woodland Blossoms", by Edward Step. Also available from Amazon: Wayside And Woodland Blossoms: A Guide To British Wild-Flowers.
There are no less than eleven native species of St. John's Wort, all characterized by a neat habit, clean-cut leaves without stalks, yellow flowers in cymose clusters, and a multitude of stamens, which are more or less joined in several bundles.
The species represented on our plate is one of the commonest, and occurs in copses and hedgebanks throughout the kingdom, as far north as Sutherland, flowering from July to September. It is very erect in habit, the stems two-edged, pale brown and smooth, two or three feet high. If the leaves are held up to the light it will be found that the veins (but not the reticulations) are pellucid, and that the leaf is thickly dotted with pellucid glands. The flowers are 1 to ¼ inch in diameter. The calyx, corolla, and sometimes leaves are more or less marked with black dots and lines. The sepals and petals are each five in number; the ovary large, pear-shaped, surmounted by three long styles, which are longer than the ovary. The stamens joined in three bundles by their bases only. Sepals glandular.
Among the other British species are:
I. Square-stalked St. John's Wort (H. tetrapteruni). Stem with four narrow wings, 1 to 2 feet, leaves broader than in perforatum, but the glands, veins and reticulations are pellucid. Styles shorter than the ovary. Flowers dense, ½ to ¾ inch, across. Moist places, July and August.
St John's Wort.
Hypericum perforatum. - Hypericineae. Hop Trefoil.
Trifolium proeumbens. - Leguminosae. -
- Leguminosae. II. Trailing St. John's Wort (H. humifusum). Stems slender, compressed, prostrate, not exceeding a foot. Leaves small, oblong; glands pellucid; the margins are often marked with black glands, and are sometimes rolled back. Flowers, ½ inch across. Sepals unequal. Styles very short. Commons and wastes. July and August.
III. Small Upright St. John's Wort (H. pulchrum). Stems slender, round, smooth, erect. Leaves heart-shaped, with pellucid glands. Sepals small, oblong, with black glandular teeth. Petals yellow, tinged with red, and edged with black glands. Styles short; anthers red. Flowers ¾ inch, loose panicles. Dry woods and heaths. June and July.
IV. Hairy St. John's Wort (H. hirsutum). Stem erect, round, downy. Leaves large, with short stalks, downy beneath, pellucid glands. Sepals very narrow, half length of petals, with black glandular teeth. Woods and thickets, especially on chalk. July and August.
V. Tutsan (H. androsaemum). Stem shrubby, compressed, 2 feet high. Flowers few, f inch across. Sepals unequal, glandular, except margin. Petals and stamens not permanent. Stamens in five bundles. Styles shorter than stamens. Hedges and thickets. July to September.