Xysmalobium undulatum is a robust geophytic herb, 0.5–2.0 m tall. It sprouts annually from a rootstock in spring and dies back in winter. The hairy leaves are large, almost stalkless and heart-shaped. Many-flowered, stalked inflorescences develop in the axils of the leaves. Flowers are cream-green to yellow; the fruit is large, an inflated follicle, covered with long curly hairs. All parts of the plant exude a milky sap when damaged.
This unusual shrub normally occurs in seasonally damp areas. It is very important from en ecological perspective, since it is the host plant of many butterflies. Keep dry in winter.