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.
Annual or biennial herbs. Leaves lobed or pinnatifid, usually viscid. Flowers regular, axillary. Calyx urceolate, 5-lobed. Corolla campanulate or funnel-shaped. Stamens 5, declinate. Fruit a 2-celled many-seeded capsule, swollen at the base, and constricted in the middle, and splitting transversely near the top. There are twelve species, found in warm and temperate parts of the Old World. The etymology of the word is obscure.
1. H. niger. Henbane. - This plant is either annual or biennial, and is merely included here on account of its medicinal and poisonous properties. It is a branching viscid foetid herb with hairy lobed or toothed leaves and sub-sessile yellowish flowers veined with purple. These characters taken with those given above will be sufficient to distinguish it, as no other species grows wild or is generally cultivated in this country.
Mandragora autumnalis, syn. M. officinalis, is a hand-some allied herbaceous plant with large fleshy roots, sinuate tufted radical leaves, and solitary scapose deep blue flowers, appearing in Autumn.