This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Like most leguminous plants included in this work this is not represented amongst the Early Glacial floras. It is a plant of the North Temperate Zone found in Europe, West Asia, North Africa. In Great Britain it is absent from the counties of Worcester, Brecon, Radnor, Carmarthen, Cardigan, Montgomery, Carnarvon, Anglesea, Renfrew, Lanark, and elsewhere, and in Scotland it only occurs in Berwick, Haddington, Edinburgh, Fife, Stirling, Forfar, and Dumbarton, growing on sandy shores and dry pastures.
Rest Harrow is an upland plant which is fond of rough, scrubby pasture, usually indicating rather bare unproductive ground. For this reason it is, like Gorse in some parts, burned and rooted up in order to get rid of it. Hillsides of medium elevation are the usual station for this plant, though it may be found on sandy shores also at a lower level.
It is a shrubby plant, with erect or prostrate then ascending hairy stems, with stolons or trailing shoots, with numerous branches, downy, and bearing long spines, smooth or gummy. The leaves are in threes below,1 above lance-shaped, coarsely toothed. The hairs may be scattered or lie in two opposite rows.
The solitary rose-coloured and white flowers are borne in the axils or in pairs, either stalkless or shortly stalked. The standard is streaked with red. The corolla exceeds the calyx, the keel and wings being equal. The pods are less than the calyx in length, downy, with seeds with raised points.
1 Or the lateral leaflets may be absent.
The plant is from 1 ft. to 18 in. in height. June, July, August are the periods during which the flowers are in bloom. The plant is perennial and increased by division.
The flower is similar to that of Lotus. It has the piston-mechanism. The alae or wings on which the bees alight act as levers to depress the carina or keel, and fold over its upper part, being united by two projections, directed downwards and upwards, which fit into deep grooves. Two lobes on the upper margin of the alae lie over the column of stamens. The alae do not cohere, but the upper borders of the carina do at first, forming a tube, and leave a small opening only at the tip, where the pollen is pushed through a small gap. The stamens are monadelphous or attached. Honey is not secreted. The stamens are thickened at the end, the outer ones most, but the inner produce more pollen. The visitors are Apis mellijica, Cilissa leporina, Anthophora quadrimaculata, Bombus lapidarius.
Photo. Flatters & Garnett - Rest Harrow (Ononis Spinosa, L.)
In the Rest Harrow the seeds are dispersed by the plant's own mechanism. The pod is 1-4-celled and 2-valved, and when contracted when dry it expels the seeds for a short distance.
Indicative of barren ground, Rest Harrow is mainly a sand plant, requiring a sand soil derived from older rocks, chiefly arenaceous, or stony ground derived from Precambrian or granitic rocks.
A mildew Peronospora trifoliorum is parasitic on it. The beetles Apian ononis, Psammobius porcicollis; the Lepidoptera, Oak Eggar (Lasiocampa trifolii), Bordered Sallow (Heliothis marginata), Bordered Straw (H. peltiger), Satyr Pug (Eupithecia satyrata), Gracil-laria ononis, Pterophora phaeodactyla, P. acanthodactylus, Grapholita citrana; many Heteroptera, Therapha hyoscyami, Metacanthus punctipes, Calocoris chenopodii, Orthocephalus saltator, Orthotylus ochrotrichus, Dicyphus globulifer, D. annulatus, Macrotylus solitarius, M. payklutii, Hopiomachus thunbergii, Macrocolus hortulanus; and the Homopteron Deltocephalus atriformis, infest this plant.
Ononis, Theophrastus, is from the Greek onos, an ass (because they are said especially to like it), and spinosa refers to its spiny nature.
Rest Harrow is called Whin, Cat Whin, Finweed, Ground Furze, Harrow Rest, Horse's Breath, Lady-whin, Wild Liquorice, Rassels, etc.
This thorny plant is troublesome in cornfields, having ligneous stems and thick roots. All cattle leave it, but horses eat it freely. It is easily cultivated.
Essential Specific Characters:76. Ononis spinosa, L. - Stem erect, spinous, hairy, shrubby, leaflets oblong, flowers rosy-pink, wings less than the keel, pods longer than the calyx, seeds tuberculate.