Milk thistle (Silybum marianum) can be a pain if it's growing in your yard.It's non-native and can be an invasive plant, as Keri Wilson, horticulturist and writer for Garden Media Group, points out, ...

As a plant, milk thistle has bright magenta or purple flowers surrounded by large, prickly leaves, "which expel a milky white sap when they are crushed, ... It's extracted from the plant's seeds.

Milk thistle is a common weed also used as a supplement in herbalism and nutrition, deriving its name from the milk-like sap it contains. The seeds of the plant contain various flavonolignans ...