Leaves: The leaves and stems are set with sharp hypodermic needles ready to inject a stinging chemical. The elliptical leaves are sharply serrated on the margins. Veins below are conspicuously raised.

Flowers: Male and female flowers occur separately on the same plant. The female flowers have conspicuous fan-shaped bracts.

Habit: Tall, leafy, largely herbaceous, and occasionally reaching 1.5 m.