What is Isatis?

Isatidis is a genus of flowering plants in the Brassicaceae family, native to the Mediterranean region of East to Central Asia.Its generic name, indigo, is derived from the ancient Greek word for plant, ἰσìτις. The genus includes Isatis tinctoria.Asian species are particularly difficult to identify due to their extremely variable morphology; the only reliable diagnostic feature is the ripe fruit.They are (usually) biennial or perennial herbaceous plants, usually blue in color, glabrous or tomentose, with erect stems branching.

Descriptions 

They are annual, biennial, or perennial, branched herbaceous plants, usually glabrous and glaucous, with the exception of siliques. Basal leaves generally elliptic-oblong, sessile; sessile cauline, round to elliptic-oblong.The hermaphroditic flowers are four-petaled double perianths.Four sepals ascend to erect.Four yellow to off-white or lilac-white petals at least as long as sepals.They have six stamens with very small egg-shaped or elongated round anthers. There are nectary glands. Racemes branched or paniculate, bracteate, inflorescences, often reaching lax and elongated in fruit.Fruit usually linear siliques, oblong-cuneate to subround, indehiscent, laterally flattened, unilocular, rarely to conspicuously winged, glabrous or with fine hairs.

Use as Chinese medicine

The root of the woad plant is used in traditional Chinese medicine to make a medicine known as Banlangen (bǎnlán'gēn Banlangen), which is said to have antiviral properties.Radix isatidis is used in China as a herbal tea for colds and tonsil ailments.When used as a tea, it is brown in color and (unlike most traditional Chinese medicines) has a slightly sweet taste.

Invasive noxious weeds

In some places, this plant is classified as a non-native and invasive weed.It is listed as a noxious weed by the departments of agriculture in several states in the western United States: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.In Montana it has been the target of widespread and largely successful eradication attempts.