Chlora perfoliata[1] Blackstonia perfoliata or more commonly known as the yellow-wort is a species of flowering plant in the family Gentianaceae found around the Mediterranean Basin, but extending into northwestern Europe.

Yellow-wort grows 10–50 cm (3.9–19.7 in) tall, with stiff, branching stems.

The leaves are glaucous, opposite and entire, the upper ones perfoliate, being united at the base.

It bears terminal cymes of bright yellow, stalked flowers, 1–1.5 cm (0.39–0.59 in) across.

[2] Pathogens affecting B. perfoliata include Peronospora chlorae.