This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
A small group of aquatic and marsh herbs with radical or whorled entire or deeply cut often bladdery leaves. Flowers scapose, solitary, spicate or racemose. Calyx inferior, persistent, bilabiate or regularly 5-toothed. Corolla deciduous, personate or bilabiate. Stamens 2, opposite the lateral sepals, inserted on the corolla or hypogynous. Capsule 1-celled; seeds minute and numerous, attached to a free basal placenta. This order contains 4 genera and about 150 species. There are two British genera, which may be introduced into the garden as objects of curiosity. Pinguicula vulgaris, Butter-wort, is a bog plant with rosulate entire radical leaves and erect axillary one-flowered naked scapes. The flowers are purplish, with a ringent spurred corolla and stamens inserted at the base of the tube. The variety grandiflora is the handsomest. The generic name is from pinguis, fat, from the appearance of the foliage. Utricularia is a genus of floating herbs with divided vesiculate leaves and personate spurred yellow flowers having the stamens inserted at the base of the lower lip. There are three species found in Britain, but neither of them is common. Name from utriculus, a bladder, in allusion to the leaves.