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.
Another of those Arctic plants not found in early deposits is Cow-wheat. To-day it is found in the Arctic and N. Temperate Zones in Europe (except Spain, Italy, Greece, Turkey), and in Siberia. Cow-wheat is widespread in distribution, growing in all the counties (except Hunts, Cardigan, Isle of Man, Shetlands), as far north as the Orkneys, and up to 3000 ft. in the Highlands. It is a native also of Ireland.
One has to look in the exact habitat of Cow-wheat to come across it, a remark almost a truism and applicable to every other plant in some degree, but especially here. That is to say it is local, choosing a peculiar type of station. Common Sylvan Cow-wheat, while an ericetal species, is more often to be found in damp localities occurring in woods and copses, and sometimes on ground surrounding streams or other tracts of water.
Cow-wheat has a sub-erect, square, weak, wavy stem, which is provided with more or less spreading branches issuing from the base. The leaves are narrowly lance-shaped, in opposite pairs, stalkless, smooth, or downy with two rows of hairs, dark-green, the base heart-shaped sometimes, the margin entire.
The flowers are pale-yellow, large, and spreading. They are borne in the axils of the leaves and in pairs turned all one way. The bracts are toothed below, spear-shaped. The corolla is irregular, four times the length of the calyx, and closed, with a projecting lower lip. The calyx is smooth, and the teeth equal the tube. The capsule is egg-shaped and depressed, like wheat, hence the first Greek name. It is said to turn bread black.
Cow-wheat is about 1 ft. to 18 in. high. The flowers bloom in June and up to September. The plant is annual, propagated by seeds.
The four anthers lie close together, and form a pollen reservoir, which is opened by touching the pointed appendages or teeth at the lower end of each anther-lobe, unlocking the reservoir. The honey lies at the base of the ovary, opposite the lip, which is expanded into a round, fleshy body with grooves each side. The honey rises 2-3 mm. in the tube, which is 14-15 mm. long, and is protected by hairs from the rain. Without inserting its head an insect needs a proboscis 14-15 mm. long, but at the anterior end the corolla is expanded and admits a bee's head, except the hive-bee, Bombus terrestris, and a few others.
The flowers are visited by Honey-bees, Bombus, Megachile, Oxycera.