Perennials with usually very large radical leaves on long petioles, and an erect branched somewhat leafy inflorescence, in some species furnished with large sheathing bracts. Flowers small, white, yellowish, or pink. Perianth composed of six petaloid subequal segments. Stamens 9. Fruit triangular, winged. Natives of various parts of Asia, especially the western district. The name is said to be derived from Rha, the Russian name of the river Wolga, on the banks of which a species of Rhubarb abounds. The species cultivated for their fleshy petioles are R. Rhaponticum and R. undulatum (fig. 206).

Fig. 206. Rheum undulatum. (About 1/20 nat. size.)

Fig. 206. Rheum-undulatum. (About 1/20 nat. size.)

1. R. Emodi. - A handsome species with large slightly rugose leaves having prominent red nerves. Flowers yellowish white, appearing in Summer. Tartary.

2. R. palmatum. - This species is readily distinguished by its deeply divided rough foliage. Also from Tartary.

3. R. Ribes. - This has large rounded cordate or reniform scabrous leaves and bright scarlet fruits. A native of Western Asia.

R. nobile is a magnificent plant from the mountains of Sikkim, probably not in cultivation at the present time. It is a tall-growing species having large leafy coloured bracts on the flower-spikes.

The genus Rumex, Dock, is distinguished by its perianth of 6 segments, the three inner segments usually enlarging, 6 stamens, and trigonous fruit. R. Hydrolapathum, with oblong-lanceolate leaves on long petioles, is a distinct indigenous .species inhabiting ditches and ponds.