- Botanical name: Rheum officinale
- Common name: Rhubarb root and rhizome
- Literal name translation: big yellow
- Family: Polygonaceae, knotweed or buckwheat family
- Part used in Chinese medicine: root and rhizome
- Major Chinese medicine actions:
- Drains heat, purges accumulations, cools blood,
invigorates and dispels blood stasis
Photo Credits: (top to bottom)
Photo 1: Rheum officinale; 06/2008; author C. Micleu; permission Jade Institute
Photo 2: Rheum officinale; 10/2004; Kurt Stueber; permission under GFDL
Photo 3: Rheum palmatum; 02/2007; author Wayne Boucher; permission under GFDL
Growing and Propagation
In China, Rheum plants are often cultivated in high mountain areas as they like full sun but cool climates and an average yearly temperature of around 50 degrees F. The leaves burn easily in the summer sun of warmer climates, even when provided some shade and regular watering. The plant is hardy in USDA zones 5 to 9.
When propagating by seed, it is best to plant them in autumn, or very early in the spring. Seed germination can be difficult, therefore it is best to soak them in warm water for 6-8 hours, then after straining off the water, cover them with a wet cloth until 1-2% of the seeds begin to sprout. They can then be can be planted in the ground with better results. Because the roots grow deeply, the soil should be fertile and dug well to a depth of 1-2 feet. During the growing season, the flower stalks should be pinched back before buds form in order to make the roots stronger.
Harvesting and Preparation
Roots are harvested from plants that are 3 years or older. The plants can be dug up in the fall after the leaves begin to die back, or in the spring before new leaves emerge. Roots should be cleaned, removing lateral rootlets, the root crown, and the rough outer cortex. The sliced roots should be dried very slowly in the cool sun or a over a very low fire.
For medicinal purposes, the best quality roots are compact, heavy and oily, with a yellowish brown surface. They should be aromatic and bitter tasting but not astringent, and when chewed should stick to the teeth. The root may be simply dried, or may be prepared with a variety of substances such as rice wine or vinegar, then heated in some manner. This special preparation enhances certain properties of the herb.
Long-term use of this herb should be avoided as it can cause damage to the large intestines, cirrhosis of the liver and electrolyte imbalance. The leaves of the plant should not be ingested as their high oxalic acid content render them very toxic.
There are several species of Rheum commonly used in Chinese medicine and known as Da Huang. Rheum palmatum, Rheum tanguticum, and Rheum officinale are the most common. The top and middle photos are of Rheum officinale, and the lower photo is of Rheum palmatum in autumn.