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Senecio (family Compositae) A genus of annual or perennial herbs, shrubs, and trees, many of which are succulent. The leaves are spirally arranged and alternate, without stipules. The flower heads are solitary or in corymbs, and are heterogamous. The involucral (see INVOLUCRE) bracts are in 1 row, sometimes with a few, outer, short bracts. The ray florets are flattened and female, or absent, the disc florets tubular and bisexual. The achene is ribbed and cylindrical, usually with a simple pappus. Most species are xerophytic, with either fleshy leaves and stems, or hairy with inrolled leaves. Several tree species are found at very high altitudes on east African mountains. Several species are ornamentals. Many are now widespread and noxious weeds, e.g. S. jacobaea (ragwort). There are about 1500 species, with a cosmopolitan distribution, mainly centred in S. Africa, the Mediterranean, Asia, and America.