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.
Butterwort is found in the Arctic and North Temperate regions in Arctic Europe, N. Asia, and N. America, but it is not found in any early deposits like other members of its association. In Great Britain it is absent in the Peninsula province from Cornwall, and in the Channel province occurs only in Dorset and N. Hants; in the Thames province only in Herts, Berks, Oxford, Bucks, Anglia; in the Severn province not in W. Gloucs; in S. Wales not in Radnor, Pembroke, Cardigan; in N. Wales not in Montgomery; in the Trent province not now in Rutland; in the Mersey, Humber, Tyne, and Lakes provinces; W. Lowlands; E. Lowlands not in Selkirk; E. Highlands; in the W. Highlands not in Mid Ebudes; N. Highlands and North Isles. It is rare in the south of England, and ascends to 3000 ft. in the Highlands. It is a native of Ireland and the Channel Islands.
When bogs were more numerous Butterwort was to be found in many different parts of the country, but chiefly, as now, in the north. It is fond of spongy pools amongst the wild morasses of the north, on the sides of hills, as well as at lower levels. It is associated with Sphagna, Drosera, Rosemary, Bog Pimpernel, etc.
The plant has a rosette of 8 radical leaves, 1 1/2 in. long, 3/4 in. broad, which are thick, greasy (hence the first Latin name), and fleshy. They are entire, coated with crystalline points and pale-greenish in colour, blunt, egg-shaped, succulent, prostrate, the central hollow, with a short, broad stalk. The older leaves are flat or convex, rosette-like in form. The margins are curved inwards.
The flowers are purple, large, nodding, with an awl-like spur, straight, as long as the petals, the upper lip divided into two, the lower into three. The scape is smooth and dilated. The corolla is gaping. The capsule is subglobose.
The glandular hairs on the upper surface of the leaves are of two kinds; the larger glands are circular in outline from above, thick, finely divided by radial divisions into 16 cells containing a light-green secretion. They differ in size and in the length of the stalk. The fluid is sticky, and can be drawn out into threads 18 in. long. A leaf may bear as many as 500,000 glands. Insects that alight upon them are at once caught. The leaf margin curls over, bringing the insect so imprisoned to the centre, where the glands are more numerous. Not only are insects caught, but pollen, seeds, etc., adhere to the leaves. The insects are slowly "digested" by the aid of the fluid secretion. The plant is thus insectivorous.
Butterwort is 6 in. in height. Flowers should be sought in May. The plant is a perennial, increased by division.
The flowers are open, conspicuous, and visited by bees. The stigma, which is not sensitive, i.e. does not move, is pushed up by the insect when it draws out its proboscis. A fly which enters the flower rubs against the stigma with its back, and dusts it with pollen from another flower, so bringing about cross-pollination. When it retreats it pushes back the stigma. The capsule splits open, and thus allows the seeds to be dispersed around the parent plant.
Photo. Flatters & Garnett - Butterwort (Pinguicula vulgaris, L.)
Pinguicula, Gesner, is from the Latin pinguis, fat, because the leaves are thick and unctuous; and the second Latin name indicates that it is common, which is true only relatively, i.e. where bogs exist.
Butterwort is also known as Beanweed, Bog Violet, Butter Plant, Butter-root, Clowns, Earning-grass, Eccle, Rot Sheep, Thickening Grass, Yorkshire Sanicle, Sheep-root, Sheeprot, Steep-grass, Marsh Violet, White Rot. It is called Sheep-root "because when turned up by the plough sheep greedily feed on it", and Sheeprot because it was supposed that it caused the liver-rot in sheep, a disease common on wet land where the plant grows, and caused by the Liver Fluke, Distomum hepaticum.
A writer says: "They call it white Rot, and not white roote, as Gerard saith, for the country people doe thinke their sheepe will catch the rot if for hunger they should eate thereof, and therefore call it the White Rot, of the colour of the herbe, as they have another they call the Red Rot, which is Pedicularis Red Rattle". Beanweed was given it because it comes up like a bean in the spring.
It is called Butterwort from the greasy feel of its leaves, as if melted butter had been poured on them. The name Earning Grass alludes to its property of acting as rennet, to "earn" meaning to curdle. Rot-grass is another name based on the supposed power of the plant to cause rot in sheep. Steep-grass refers also to the curdling property, "steep" being rennet in Lancashire and Cheshire, and Thickening Grass alludes also to the curdling property.
Gerarde says the juice was rubbed in cows' udders when cracked. In the north in the time of Linnaeus they put fresh leaves in reindeers' milk and strained it, and after a day or two it became tenacious, as the whey and cream do not separate. It does not act on cows' milk in the same way.
Essential Specific Characters: 245. Pinguicula vulgaris, L. - Flowering stem a scape, leaves radical, in a rosette, oblong, fleshy, with recurved margins, with crystalline points, flowers purple, corolla gaping, petals oblong, distinct.