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.
The Rest-Harrow or Wrest-Harrow is one of those plants whose presence in the pasture is said to indicate its poverty or the neglect of the cultivator. In Sussex and Hampshire it is known as the Cammock. It is a perennial low shrub, sometimes creeping near the ground, and at others growing more erect. The rootstock often creeps underground, a habit to which the plant owes its popular name, as it is said to be so tough as to wrest the harrow from the even tenor of its way. The more prostrate form is covered with viscid hairs; the more erect-growing plants are spiny. In the latter condition it is said that only donkeys will eat it, and hence its scientific name ononis, from onos, an ass, but it is open to question whether the ass has any fondness for it if he can get other food. The flowers are of the usual papilionaceous structure already described (see pp. 7, 43, 48, 50, 52, 72), and may be borne either singly or in racemes. They are pink in colour; the-petal known as the standard is very large in this species, and streaked with a fuller red. The pod is very small, and in the-hairy form is not so long as the; calyx. The flower docs not secrete honey, but in spite of this fact, it seems to be chiefly if not exclusively fertilized by bees, who are evidently fooled by its resemblance to other flowers of the same form that do offer refreshment to insect visitors. The worker-bees, however, get pollen for their pains, but the males arc sadly disappointed Rest-Harrow will be found flowering in dry wastes from June to September.
There is another species, the Small Rest-Harrow (O. rcrlinala), an annual spreading, hairy, viscid stems, only a few inches in length, stalked rosy flowers not half the size of spinosa, and a hairy pod as long as the calyx, or longer. It is exceedingly local, and has only been reported as occurring on sandy cliffs is Devon, Wigton and Alderney. Flowering in June and July.
Rest Harrow. Ononis Spinosa.