Rheum australe, synonym Rheum emodi, is a flowering plant in the family Polygonaceae. It is commonly known as Himalayan rhubarb,[1] [2] Indian rhubarb[1] and Red-veined pie plant.[1] It is a medicinal herb used in the Indian Unani system of medicine, and formerly in the European system of medicine where it was traded as Indian rhubarb.[3] The plant is found in the sub-alpine and alpine Himalayas at an altitude of 4000 m.[4]
The plant has a 1.5-2m high stem.[1] [2] Its stem is stout, red, and streaked green and brown.[1] [2] The large leaves are heart-shaped[2] or roundish with a heart-shaped base,[1] and greenish-red in colour.[2] The basal leaves can be up to 60 cm wide.[1]
It has dark reddish-purple[1] or yellow flowers in late spring to summer,[2] in densely-branched clusters, in a inflorescence up to 30 cm long. The inflorescence enlarges greatly when in fruit.[1]
According to the 2003 key in the Flora of China, this species is distinguished from other entire-leaved rhubarbs in China with leaves having a wavy or crisped margin; R. wittrockii, R. rhabarbarum, R. webbianum and R. hotaoense, by having less than 1 cm-sized fruit, purple-red flowers, and the surface of the rachis of panicle being densely pubescent. It is the only rhubarb in this group to have purple-red flowers as opposed to various shades of white.[5]
A 1947 study found plants of R. emodi a chromosome count of 2n=22, but the same study found plants labelled as R. australe to be 2n=44. It is possible that this karyotypic diversity indicates the existence of one or more cryptic species, because the polyploid forms would essentially be reproductively isolated.[6]
Native to India, Myanmar, Nepal, Pakistan, Bhutan, and Sikkim.[1] [4]
It grows on grassy or rocky slopes, crevices and moraines, forest margins, near streams and between boulders in specific zones.[4] Impatiens glandulifera in the Valley of Flowers, Uttarakhand, India.[1]
It is said to be quite hardy and readily propagated.[2]
Hydroxyanthracene derivatives are mainly emodin, chrysophanol and their glycosides.[7] Other hydroxyanthracene derivatives are rhein, aloe emodin and physcion and their glycosides.[8]