Rehmannia

original: 地黄 (Dihuang); Rehmannia glutinosa

The illustration above depicts the Rehmannia plant, a cornerstone of Traditional Chinese Medicine. This botanical illustration is rendered in the classic style of a Materia Medica original: 本草 (Bencao), designed to help practitioners identify the plant in the wild.

The plant is characterized by its distinctive foliage, which grows in a low-lying rosette. The leaves are thick, wrinkled, and covered in fine hairs. From the center of this rosette, a flowering stalk emerges. As shown in the woodcut, the plant's growth habit is sturdy and upright.

The name "Earth Yellow" refers to the plant's most valuable part: its large, succulent root. When freshly harvested, the root's flesh is a bright yellow color. In the pharmaceutical tradition, it is categorized by its preparation method:

• Fresh Rehmannia original: 鮮地黃 (xiandihuang) is used for its cooling properties to treat "heat" in the blood.
• Dried Rehmannia original: 生地黃 (shengdihuang) is used to nourish the "Yin" the cooling, fluid, and structural aspects of the body.
• Prepared Rehmannia original: 熟地黃 (shudihuang), which has been steamed with wine and dried until it turns black and sweet, is used as a powerful tonic for the blood and the "essence" of the kidneys.

Historical medical texts often place Rehmannia in the 'Superior' class of herbs because it is considered non-toxic and beneficial for longevity when taken over long periods.