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.
We have explained (page 98) in what respect the Scabious differs from the somewhat similar flowers of Compositae, and to a considerable extent that explanation will hold good for the genus Dipsacus, which is united to Scabiosa in the Natural Order Dipsaceae. There is this difference, however: in Dipsacus the flower-bracts end in long, straight, sharp points, and the involucel is four-angled. There are two British species:
I. Wild Teasel (D. sylvestris). A striking object in copse or hedgerow; its stout, angular and spiny stems rising to a height of 4 or 5 feet, and crowned by the prickly-cylindrical heads of flowers. These heads have an involucre, consisting of from eight to twelve slender rigid bracts, spiny, longer than the flower-head, curved upward and ending in a fine point. The corolla is purple, tubular, with four short unequal lobes. It is a biennial plant, and only has radical leaves during its first year, sending up the flowering stem the second season. These are stalked, lance-shaped, with a stout mid-rib, which is armed with short curved spines. The stem-leaves are opposite, not stalked, the lower couples joined together by their bases, thus forming a large cup, in which rain collects and drowns many insects that attempt to ascend the tall stem. Flowers August and September. The Fuller's Teasel (D.fullonum), of so great importance to the cloth manufacturer, is believed to be a cultivated variety of sylvestris, having the involucral bracts shorter and spreading, and the scales of the flower-heads hooked.
II. Small Teasel (D. piles us). This is a more slender plant, the stem not so tall or stout, and the prickles ending in soft hair-points. Leaves stalked, hairy. Flower-heads at first drooping, then erect; smaller, rounder, hairy, the involucral bracts shorter than the head. Flowers white. August and September, in moist hedges; not so generally distributed as sylvestris.
Dipsacus Sylvestris. - Dipsaceae. -