Native to: Afghanistan, Albania, Algeria, Altay, Angola, Austria, Baleares, Bangladesh, Benin, Botswana, Bulgaria, Burkina, Burundi, Buryatiya, Cambodia, Cameroon, Canary Is., Cape Provinces, Cape Verde, Caprivi Strip, Central African Repu, Central European Rus, Chad, China North-Central, China South-Central, China Southeast, Corse, Czechoslovakia, Djibouti, East Aegean Is., Ecuador, Egypt, Eritrea, Ethiopia, France, Free State, Gambia, Ghana, Gilbert Is., Greece, Guinea, Gulf States, Hainan, Howland-Baker Is., Hungary, India, Inner Mongolia, Iran, Iraq, Italy, Ivory Coast, Japan, Kazakhstan, Kenya, Kirgizstan, Korea, Kriti, Kuwait, KwaZulu-Natal, Lesser Sunda Is., Libya, Madagascar, Malawi, Maldives, Mali, Manchuria, Mauritania, Mongolia, Morocco, Mozambique, Mozambique Channel I, Myanmar, Namibia, New Caledonia, New South Wales, Niger, Nigeria, Northern Provinces, Northern Territory, Oman, Pakistan, Palestine, Phoenix Is., Portugal, Qinghai, Queensland, Romania, Rwanda, Sardegna, Saudi Arabia, Senegal, Sicilia, Sinai, Socotra, Somalia, South Australia, South China Sea, South European Russi, Spain, Sudan, Swaziland, Tadzhikistan, Taiwan, Tanzania, Tibet, Togo, Tokelau-Manihiki, Tunisia, Turkey-in-Europe, Turkmenistan, Tuva, Uganda, Ukraine, Uzbekistan, West Siberia, Western Australia, Western Sahara, Xinjiang, Yemen, Yugoslavia, Zambia, Zaïre, Zimbabwe.

Introduced into: Alabama, Aldabra, Argentina Northeast, Argentina Northwest, Argentina South, Arizona, Arkansas, Aruba, Bahamas, Bolivia, British Columbia, California, Cayman Is., Chile North, Colombia, Colorado, Cuba, Delaware, Dominican Republic, El Salvador, Florida, Galápagos, Guatemala, Guyana, Haiti, Idaho, Illinois, Indiana, Iowa, Jamaica, Kansas, Kentucky, Leeward Is., Louisiana, Maryland, Masachusettes, Mauritius, Mexican Pacific Is., Mexico Northwest, Mexico Southwest, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Netherlands Antilles, Nevada, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Ontario, Oregon, Panamá, Pennsylvania, Peru, Philippines, Primorye, Puerto Rico, Réunion, South Carolina, South Dakota, St.Helena, Suriname, Tennessee, Texas, Trinidad-Tobago, Turks-Caicos Is., Uruguay, Utah, Venezuela, Venezuelan Antilles, Washington, Windward Is., Wisconsin, Wyoming.

Herbs, usually annual, sometimes perennial [rarely subshrubs]. Stems prostrate to suberect, diffusely branched, terete, becoming ridged on drying, to 1[-3] m, somewhat succulent, densely hairy to glabrate. Leaves opposite, even-pinnately compound, one of each pair alternately smaller or sometimes abortive; stipules persistent, herbaceous, subulate to falcate, apex acute; petiolules very short to absent, less than 1 mm; leaflets 6-16(-20), opposite, distinct, oblong to ovate or elliptic, middle pairs largest, base oblique, apex acute or obtuse, surfaces hairy, terminal pair pointed forward. Pedicels emerging from axils of alternately smaller leaves, erect. Flowers solitary, regular; sepals caducous, 5, distinct, green, equal, margins scarious, apex acute, hairy; petals deciduous, 5, imbricate, spreading hemispherically, not twisted, usually bright yellow, rarely white, base often darker, oblong to obovate-cuneate, base not clawed, apex rounded to slightly lobed; nectary 10 glands in 2 whorls, outer whorl 5 ± 2-lobed glands, inner whorls 5 distinct or connate glands; stamens [5-]10, 5 opposite petals somewhat longer; filaments adnate at base to petals, subulate [filiform], unappendaged; anthers cordate to oblong-cordate or sagittate; ovary sessile, 5-lobed, 5-locular, hirsute with stiff, upward-spreading bulbous-based hairs; ovules 3-5 per locule; style deciduous; stigma terminal, slightly asymmetric, 5-lobed, pyramidal or globose, papillose. Fruits schizocarps, horizontally depressed, 5-angled, at maturity dividing septicidally into 5 or rarely fewer mericarps and leaving no central axis; mericarps broadly triangular, apex dorsally crested, tuberculate, spiny [or winged or rarely only tuberculate abaxially], each divided internally by oblique transverse septa into 2-5 1-seeded compartments. Seeds usually 3-5 per mericarp, white, oblong-ovoid. x = 6.