It is an annual herb, native to the Palaearctic and widely naturalised as a ruderal species in suitable disturbed habitats worldwide.

[9] Open clusters of 10 to 22 small cylinder shaped rayless yellow flower heads 1⁄4 to 1⁄2 inch (6 to 13 mm) with a highly conspicuous ring of black tipped bracts at the base of the inflorescence as is characteristic of many members of the genus Senecio.

[10] The name for the genus Senecio is probably derived from senex (an old man), in reference to its downy head of seeds; "the flower of this herb hath white hair and when the wind bloweth it away, then it appeareth like a bald-headed man"[11] and like its family, flowers of Senecio vulgaris are succeeded by downy globed heads of seed.

[8] Groundsel acts as a host for the fungus that causes black root rot in peas,[9] alfalfa, soybeans, carrots, tomatoes, red clover, peanuts, cucurbits, cotton, citrus, chickpeas, and several ornamental flowering plants; a list of flowering plants that can host their own fungus as well.

Binomial etymology Common names Senecio vulgaris is considered to be native to Europe, northern Asia, and parts of North Africa.

The United States Department of Agriculture (USDA), Natural Resources Conservation Service Plants Profile Database[22] considers it to be native to all 50 of the United States of America, Canada, Greenland, Saint Pierre and Miquelon,[1] the same USDA through the Germplasm Resources Information Network (GRIN)[23] considers it to be native only to parts of Afro-Eurasia.

[26] Individual research groups claim it is not native to areas they oversee: Florida,[27] Washington,[28] Wisconsin,[29] Saskatchewan,[30] British Columbia,[31] Missouri.

[33] Senecio vulgaris is a frost-resistant[6] deciduous annual plant that grows in disturbed sites, waste places, roadsides, gardens, nurseries, orchards, vineyards, landscaped areas, agricultural lands,[19] at altitudes up to 1,600 feet (500 m)[6] and is, additionally, self-pollinating[19] producing 1,700 seeds per plant with three generations per year.

In the United States, Senecio vulgaris has been listed as a noxious weed,[40] being both non-indigenous to most if not all of the Americas and having a reputation for being hepatotoxic to livestock[41] and to humans.

All species of the genus Senecio contain pyrrolizidine alkaloids (e.g., senecionine), a substance that when a human has chronic exposure[45] can cause irreversible liver damage.

Lesser amounts cause the liver to lose function but is not apparent until the animal is stressed (by new feed or location, pregnancy, a different toxin, etc.).

Sheep and goats have rumen bacteria that detoxify the alkaloids and are able to consume twice their body weight of this and other species of genus Senecio.

Groundsel seed numbers increased in soil during a two-year set-aside left fallow but not when there was a sown grass cover.

[9] The pathogen rust fungus or Puccinia lagenophorae and the cinnabar moth (Tyria jacobaeae) have both been used and studied in an attempt to control infestation of Senecio vulgaris.