Silphium integrifolium aka Whole Leaf Rosinweed

Silphium integrifolium is a perennial wildflower in the aster family. Its common names include rosinweed and wholeleaf rosinweed. Its native range runs from southeast Canada into northern, central, and eastern parts of the United States. It grows in prairies, fields, pastures, and glades. It also grows beside roads and rail lines. Plants form upright clumps from taproots and short rhizomes. They do not spread fast through their roots.

Garden plants often stand 2–3 feet (0.6–0.9 m) tall. Some reach 6 feet (1.8 m). Clumps spread 1–3 feet (0.3–0.9 m) wide. Strong green stems help the plant stay upright. Young stems bear hairs, which may fade with age. Rough green leaves grow in pairs without leaf stalks. Each pair turns a quarter turn from the pair below. Leaves range from narrow to oval and contain resinous juice. Their edges may be smooth or have fine teeth. Leaves can reach 0.67 feet (0.20 m) long. The plant sheds its leaves each year.

Yellow flower heads look like small sunflowers and form clusters. Each head has many central florets and about 30–40 rays. Flower heads span about 0.17–0.25 feet (0.05–0.08 m). Bloom starts in July and can last into October. Bees and butterflies visit the flowers, including bumblebees. Songbirds eat the large, flat seeds. Wind can also carry the seeds away from the parent plant.

Rosinweed grows best in full sun and well-drained soil. It accepts sand, loam, and clay, plus some light shade. Moderate soil moisture suits it, but established plants withstand drought. Sources place it in USDA zones 4–8. Growth is moderate, though young plants may take time to settle. Plants raised from seed can be slow to establish. Its taproot makes division a poor choice once established. It needs little routine care and has few serious pests. Leaf spots, rust, and downy mildew can still occur.

Use it in meadows, native gardens, or groups with room to spread. It can stand behind shorter perennials in a border. Self-seeding may make it too weedy for small gardens. Large grazing animals eat its stems, leaves, and flowers. Researchers are developing it as a seed-oil crop. PFAF reports past root use for pain from injuries. That source lists no known hazards, rather than confirmed safety.