This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this plant is cultivated and waste ground and fields. The habit is erect. The stem is branched, with stinging hairs. The leaves are opposite, elliptic, ovate to oblong, stalked, coarsely toothed, the teeth few and the terminal one oblong. The flowers are few, arranged in axillary panicles or spikes in pairs, which are simple, shorter than the leaf-stalk. The plant is usually monoecious. The flower-stalks are long or short. The seeds are oblong. The plant is 9 in. to 2 ft. high, flowering from June to September, and is a herbaceous annual.