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.
Perennial or annual herbs. Leaves opposite, often ribbed. Flowers regular, solitary or cymose, often very brilliantly coloured. Calyx 4- or 5-lobed or spathaceous. Corolla funnel-or salver-shaped, 4- or 5-lobed, or rarely more; throat of the tube naked or bearded, or furnished with scales. Stamens 4 or 5. Fruit a 2-valved 1-celled many-seeded capsule. This is an extremely beautiful genus of plants, comprising about 150 species, found in nearly all temperate and alpine regions. Gentiana is the classical name for some of the species.
1. G. acaulis (fig. 169). Grentianella. - This is one of the most beautiful and at the same time one of the easiestgrown species of the genus. It is a perennial, attaining a height of 2 to 4 inches, bearing solitary terminal intense blue flowers of large size. The throat of the corolla is naked, and the calyx-lobes closely applied to the corolla-tube. A native of the Alps, flowering in Spring or Summer. G. excisa, including G. alpina, is very closely allied to the foregoing, but differs in its spreading calyx-lobes.
Fig. 169. Gentiana acaulis. (1/4 nat. size.)
2. G. verna. - A dwarf tufted species resembling the last in habit and other particulars. But in this the azure-blue flowers are smaller, the calyx-tube is 5-winged, and the lobes small and erect. Corolla-tube narrower, with the limb about an inch in diameter, furnished with bifid scales at the throat between the lobes. This is a native of the North of England and some parts of Ireland, as well as the Continent.
G. Pyrenaica is an alpine species near the last, with a 10-lobed corolla, the lobes alternately larger and smaller; and G. Bavarica is another closely-allied blue-flowered species, in which the radical leaves are not rosulate, and the throat of the corolla is naked.
3. G. cruciata. - An erect-growing perennial about a foot high, bearing clusters of comparatively small blue flowers in the axils of the upper leaves. The corolla is 4-lobed and naked at the throat. Leaves decussate, lanceolate, 3-nerved, sheathing at the base. A native of mountainous parts of Central and Southern Europe.
4. G. asclepiadea. - Near the last in size and inflorescence, though there are rarely more than 2 flowers from the axil of each leaf, and usually only one. Leaves relatively large, sessile, ovate-lanceolate, acuminate, 5-nerved, rough on the margin. Flowers deep blue, appearing in Summer. Corolla 5-lobed, naked at the throat; tube broadly club-shaped. A handsome plant and one of the best for borders and general cultivation. There is a variety with white flowers. It is a native of the Alps and Apennines.
5. G. lutea. - This is a tall-growing plant from 3 to 4 feet high with large ovate or elliptical nerved leaves and dense clusters of yellow flowers in the axils of the upper leaves. Corolla 5-lobed, throat naked, lobes often having 3 rows of dark lines or dots. A native of the mountainous parts of Central Europe, flowering with us in June or July. This species furnishes much of the officinal Grentian-root.
6. G. Saponaria, syn. G. Catesbai of some authors. - An erect free-growing species with ovate-lanceolate or obovate leaves narrowed at the base and rough on the margins. Flowers light blue, clustered in the axils of the upper leaves; corolla-tube broad, limb 5-lobed; lobes small, erect, alternating with bifid fringed appendages. A native of North America, flowering towards the end of Summer.
7. G. Andrewsii, G. Saponaria of some writers, and perhaps oftener seen under that name in gardens. It differs from the preceding species in its broader foliage and inflated corollas which are nearly closed at the mouth and destitute of a limb, the primary lobes being absent and replaced by the fringed and toothed appendages. A native of North America.
G. septemfida has spotted white and blue flowers; G. gelida has campanulate purplish blue flowers; G. punctata has them pale yellow with dark spots; and G. Pneumonanthe var. alba has large white flowers.
Sabbatia campestris is an elegant tender annual from Texas, growing about a foot high and bearing clusters of small rose-coloured flowers with a yellow centre; S. stelldris and S. chloroides are hardy slender North American annuals with rosy purple or white flowers. The corolla in this genus is rotate, with from 5 to 12 divisions and an equal number of stamens.
Swertia perennis is a European perennial with quadrangular smooth stems about a foot high, elliptical leaves, and dull violet flowers. Corolla rotate, 5-lobed; lobes fringed.