Vernonia noveboracensis

Ironweed earns the name twice over. The stems are stiff enough to stand through a hurricane season without staking, and the seedheads that follow the flowers rust to the exact color of weathered iron. But the reason to grow Vernonia noveboracensis is the purple: not the tidy lavender of garden asters but a saturated, almost fluorescent violet that arrives in late July and holds into October, riding five to eight feet up on strong green stems above a mass of long, finely toothed leaves. Few native perennials carry a color this pure so late in the year.

The genus honors William Vernon, an English botanist who collected in Maryland in 1698 and carried the seeds home to Cambridge; Schreber formally established Vernonia in 1791, long after Vernon had died. The epithet noveboracensis is botanical Latin for "of New York," a common enough tag on species first described from the northeastern colonies, though this ironweed is far more abundant southward, running through the Carolinas and Georgia into Alabama and Florida. In the wild, look for the plant in wet meadows, ditches, streambanks, and low pasture, often alongside Joe-pye weed, for which ironweed is regularly mistaken at a distance.

Ecologically this is a heavyweight. The flowers are a late-season nectar station for monarchs and swallowtails staging for migration, and the genus supports a pollen specialist, the denticulate longhorn bee (Melissodes denticulatus), that visits little else. Songbirds take the seed through fall. The hollow dead stems become winter nesting sites for small native bees, which is a good argument for cutting old growth back to a foot or two rather than to the ground and letting the stubs stand until they collapse on their own. North Carolina named the species Wildflower of the Year in 2004, and deer, notably, leave the bitter foliage alone.

That bitterness is the ethnobotanical thread. Cherokee practice used root infusions for pain after childbirth, for stomach ulcers, and for loosening teeth, while leaf teas served as a blood tonic and for women's complaints. The whole genus runs bitter with sesquiterpene lactones, the same class of compounds that makes the African ironweeds a staple of traditional medicine and a continuing subject of pharmacological research.

In the garden, give ironweed sun and moisture and then step back. Rain gardens, pond margins, stormwater basins, wet meadows, and the back of a deep border all suit, and the classic companions share the same wet feet: swamp sunflower, swamp milkweed, swamp rose mallow, and a matrix of switchgrass or big bluestem. Gardeners who find eight feet excessive can cut the stems back by half in early July for a shorter, bushier plant, and cutting a group to varying heights gives a longer, layered bloom. Ordinary garden soil that stays reasonably moist is enough, and established clumps handle dry spells better than the swampy provenance would suggest.