Cup plant, named for the cup-shaped depression formed where opposing leaves meet
the stem, is another member of the very large aster family. It is a North American native.
Identification: Plants are 4-10′ (1.2-3 m) tall,
on single stalks that branch only near the flowering top. They could be mistaken for a type
of sunflower, except for the unusual leaves. The stem is thick and hairless,
four-sided, and green or purple. Leaves are opposite, joined to each other at the stems,
producing a depression between them that holds water. The trapped water often attracts birds.
Leaves are rough to the touch,
and coarsely toothed. Flowers have a dark yellow central disk surrounded by 18-40 bright yellow petals ("ray florets").
They appear from July to October. Fruits are egg-shaped achenes ¼-½″ (7.6-12 mm) long, with wings.
From Britton, Nathaniel Lord, and Brown, Addison, An illustrated flora of the northern United States, Canada and the British Possessions, 1913; scanned by the Natural Resources Conservation Service.