As a matter of fact, woad is the common name of Isatis tinctoria, which is one of the members in the family Brassicaceae. This herb has high pharmaceutical values and the main medicinal parts are its roots and leaves. And in another our previous article, isatis root or Ban Lan Gen has already been covered. The leaf is also known as indigo leaves or isatis leaves. In terms of TCM, it refers to the leaf of Isatis tinctoria L., I. indigotica Fort., Baphicacanthus cusia (Nees) Bremek. [Strobilanthes flaccidifolius Nees], Clerodendron cyrtophyllum Turcz., and Polygonum tinctorium Lour. All the leaves of above-mentioned species can be used as a raw material for manufacturing indigo. However, when it comes to the roots, the Indigofera tinctoria is the only one that can’t be used medicinally.

And Isatis indigotica Fortune is the most common one medicinally. As a biennial herb, the woad plants are 50 to 100cm in height, smooth, and covered with pruina. The fleshy root is nearly conical, in diameter of 2 to 3cm, 20 to 30cm long, and with soil yellow surface, short stripes and a few short fibrous roots. Basal leaves are in the shape of rosette, with oblong to broadly oblanceolate leaf blade, 5 to 15cm long, and 1.5 to 4cm wide. Leaf comes with obtuse apex and entire or slightly corrugated margin. The inflorescence is raceme, terminal or axillary, forming cone at branch tip. Silicle is nearly oblong, flattened, glabrous, and with membranous wings on the edge. Seed is only one, oblong, and light brown. It usually blooms from April to May and fruits from May to June.

Leaf contains indigo or indigotin, isatan B, indirubin, and other inorganic elements such as iron, titanium, manganese, zinc, copper and diamonds, nickel, selenium, chromium, and arsenic. The hydrolysis of isatan can change it into indigo and D-xylo-5-hexulofuranosonic acid.

MODERN PHARMACOLOGY 
1. Antibiotic effect. In vitro test of the isatis leaf decoction showed that it has a certain inhibitory effect on Staphylococcus aureus, Streptococcus, Neisseria meningitidis, Streptococcus pneumoniae, catarrhal bacteria, Salmonella typhi, E. coli, Haemophilus influenza, diphtheria bacilli and Shigella.

It inhibits also encephalitis B virus, mumps virus, and influenza virus. In addition, it kills leptospira.

2. Anti-endotoxin effects. In vivo experiments showed that isatis leaves have anti-endotoxin effect on E. coli O111B4.

3. Indirubin has a higher inhibitory rate on leukemia L7212 in mouse.

Woad Leaves

POPULAR ISATIS LEAVES RELATED HERBAL FORMULAS 
Isatis leaf is known as cold and bitter in properties in TCM practice. It covers 4 meridians, including liver, heart, stomach, and spleen. Its typical functions are to clear heat, remove toxicity, and cool blood to eliminate spots. Its key indications and uses are hyperpyrexia and polydipsia in pyreticosis, coma, rash, spitting blood, bleeding from five sense organs or subcutaneous tissue, jaundice, Diarrhea and dysentery, Erysipelas, Chronic Pharyngitis, mouth sores, and mumps. Usual dosage in decoction is from 10 to 15 grams. Or it can be consumed in juice by smashing.

It is widely used in so many ancient formulas and some of them are listed as follow, to name but a few.

1. Prevent encephalitis and meningitis by combining Da Qing Ye 25g and Huang Dou (Soy Bean) 50g. Decoct them and take it once a day for straight 7 days. – From Jiang Xi Cao Yao (Jiangxi Herbal Medicine)

2. Treat epidemic eruptive disease accompanied with spots by formula of Da Qing Ye, Gan Cao (Licorice Root), Jiao (Glue), and Chi (fermented soya beans). – From Bu Que Zhou Hou Fang (Handbook of Prescriptions for Emergencies).

3. Treat epidemic high fever, headache, and with sores all over the body with the prescription of Da Qing Tang, including Da Qing Ye, Zhi Zi (Gardenia), Xi Jiao (Rhinoceros Horn), and Chi. – From Yan Nian Fang (Prescriptions for Prolonging Life).