Cup Plant (Cup Rosinweed; Carpenter's Weed)

Silphium perfoliatum


Photo of cup plant flowerhead.
Cup plant is notable for its square stems and opposite leaves that fuse around the stem to form a leafy cup.
Beverly Turner, Jackson Minnesota,

Asteraceae (daisies, sunflowers)


Cup plant is a tall perennial herb with square stems. Flowerheads numerous, to about 3 inches wide, yellow, with 18–35 ray flowers to 2 inches long. Blooms July–September. Leaves mostly opposite, to 1 foot long, with wavy, coarsely toothed margins (not lobed), rough on both sides, oval to triangular, covered with dots. Bases of opposite leaves are joined around the stem, forming a leafy cup that holds water.

Similar species: There are 6 Silphium species recorded for Missouri. Of these, cup plant, starry rosinweed (S. asteriscus), rosinweed (S. integrifolium), compass plant (S. laciniatum), and prairie dock (S. terebinthinaceum) are relatively common. Cup plant is identified by its square stems and unlobed leaves that join to form cups around the stem.


Height: 4 to 8 feet.


Photo of cup plant showing square stem and clasping leaf bases.
Cup Plant (Cup Rosinweed) (Stem)
Square stems, a famous characteristic of the mint family, is also a way to identify cup plant, which is in the sunflower family.


Photo of cup plants growing near the edge of a field.
Cup Plant (Cup Rosinweed)
Cup plant occurs in low areas near water, edges of fields, and waste places, sometimes forming dense colonies.


Photo of cup plant showing large, opposite, perfoliate leaves.
Cup Plant (Cup Rosinweed) (Leaves)
Cup plant has perfoliate leaves. Two opposite leaves clasp the stem and fuse together, so it looks like a single leaf with a stem through it.


Photo of cup plant showing seeds forming in spent flowerheads.
Cup Plant (Cup Rosinweed) (Seeds)
In cup plant, the ray florets are pistillate and turn into flattened brown seeds. The disk florets only produce pollen.
Habitat and conservation

Occurs on banks of streams and rivers, bottomland forests, and margins of ponds and lakes; also along edges of crop fields, railroads, and roadsides. Look for it in low areas near water and waste places. To some people, this species is a common weed; in fact, is considered a noxious plant in Connecticut. It is not problematic in Missouri. Some people cultivate it as a coarse, tall background plant in native wildflower gardens. In Michigan, it is classified as threatened.

image of Cup Plant Cup Rosinweed Carpenter’s Weed distribution map
Distribution in Missouri

Scattered nearly statewide; uncommon in the Mississippi Lowlands.


It’s not an accident that rosinweeds are in their own genus, Silphium, and not in the genus Helianthus (sunflowers). Yet some of them look much alike. How can you tell the difference? The disk florets in rosinweeds are essentially staminate (male) and therefore don’t create seeds, just pollen; but the disk florets in sunflowers, as most of us know, create seeds. The petal-like ray florets in rosinweeds are pistillate (female) and turn into seeds, while those in sunflowers are sterile.

Human connections

Silphiums are called rosinweeds because of the gummy resin that oozes from damaged tissues, which was used by Native Americans and pioneers as a kind of chewing gum. Indians also used these plants for a variety of medicinal applications. The name carpenter’s weed alludes to the square stems.

Ecosystem connections

Many insects visit and pollinate the flowers. Birds, including goldfinches, eat the seeds and sip water collected in the leaf cups. Many animals find shelter in this plant’s dense colonies. A variety of wasps are obliged to deposit eggs in rosinweeds; their gall-forming larvae grow in the stems.