Common nightshade and Nightshade

Common nightshade noun - Eurasian herb naturalized in America having white flowers and poisonous hairy foliage and bearing black berries that are sometimes poisonous but sometimes edible.

Nightshade and common nightshade are semantically related. In some cases you can use "Nightshade" instead a noun phrase "Common nightshade".

Nightshade noun - Any of numerous shrubs or herbs or vines of the genus Solanum; most are poisonous though many bear edible fruit.

Common nightshade and nightshade are semantically related. Sometimes you can replace phrase "Common nightshade" with "Nightshade", this terms are similar.