Polygonacce—-Rheum. 385 
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. Rhapénticum and R. undulatwm (fig. 206). 
1. &. Emodi.—A handsome species with large slightly 
rugose leaves having prominent red nerves. Flowers yellowish 
white, appearing in Summer. Tartary. 
2. R. palmatum.—tThis species is readily distinguished by 
its deeply divided rough foliage. Also from Tartary. 
3. R. Ribes.—This has large rounded cordate or reniform sca~- 
brous leaves and bright scarlet fruits. A native of Western Asia. 
A. nobile is a magnificent plant from the mountains of 
Sikkim, probably not in cultivation at the present time. Itisa 
tall-growing species having large leafy coloured bracts on the 
flower-spikes. 
The genus Rwmex, Dock, is distinguished by its perianth 
of 6 segments, the three inner segments usually enlarging, 6 
stamens, and trigonous fruit. R. Hydrolépathum, with oblong- 
lanceolate leaves on long petioles, is a distinct indigenous 
species inhabiting ditches and ponds. 
Orper XC.—NYCTAGINACEZ:. 
Annual or perennial herbs, rarely shrubs, usually swollen at the 
joints. Leaves opposite or alternate, and frequently unequal. 
Flowers bisexual, capitate or solitary. Perianth inferior, 
coloured, tubular or funnel-shaped, constricted in the middle. 
Stamens definite, hypogynous. Fruita 1-celled 1-seeded utricle 
enclosed in the enlarged often indurated tube of the perianth. 
Seeds adhering to the walls of the ovary. There are about 16 
genera and 100 species, chiefly tropical. 
1, ABRONIA. 
Herbs with opposite simple petiolate leaves and capitate 
flowers surrounded with a finely divided involucre. Perianth 
funnel-shaped or salver-shaped. Stamens 5. A small genus 
of North-western American plants. The name is said to be 
from a@@pos, elegant, in allusion to the involucre. 
CC 
