Description from Flora of China
Herbs perennial or annual, erect, rarely stoloniferous, decumbent, or rarely scandent, rhizomatous. Stems usually leafy, rarely subscapiform. Leaves simple; radical leaves usually petiolate, not auriculate, deltoid, lyrate or pinnately divided; stem leaves usually sessile, pinnately veined, basally often auriculate, lyrate or pinnately lobed, rarely unlobed, ± dentate. Capitula rarely solitary, axillary, usually few to numerous, arranged in terminal simple or compound corymbs or thyrses, heterogamous and radiate or homogamous and discoid, erect or nodding, usually pedunculate. Involucres calyculate, hemispheric, campanulate, or cylindric; receptacle flat; phyllaries 5-22, usually free, rarely connate to middle or above, herbaceous or leathery, margin scarious or membranous. Ray florets absent or 1-17(-24); lamina yellow, usually conspicuous, sometimes minute, 2-9-veined, apically usually 3-denticulate. Disk florets 3 to many; corolla yellow; limb funnelform or cylindric; lobes 5. Anthers oblong to linear, usually shortly obtuse-auriculate, rarely ± caudate with tail to 0.25 × as long as antheropodium; antheropodia balusterform, basally slightly to markedly dilated, with enlarged basal lateral cells; endothecial cell wall thickenings numerous, radial (inner anticlinal), cells often elongated. Style branches truncate or less often convex, with rather obtuse semicircle of marginal papillae, not appendiculate and devoid of a central tuft of longer papillae. Achenes cylindric, ribbed, glabrous or pubescent, epidermal cells smooth or papillose. Pappus capillary-like, uniform or sometimes dimorphic by presence of apically fluked hairs, white, straw-colored, or reddish brown, sometimes absent from ray florets or rarely from all florets.
The generic concept provided here is considered to cover Senecio s.s. plus a fringe of taxa that can be considered peripheral to Senecio s.s. but not extending to Senecio s.l. (fide Vincent).
A recent molecular taxonomic study (Pelser et al., Taxon 56: 1077-1104. 2007) suggests that certain elements should be removed from Senecio, namely, S. ser. Extremiorientales and S. ser. Erucifolii (to genus Jacobaea Miller), S. sect. Madaractis (to genus Madaractis), and S. sect. Flexicaules (to a new, as yet undescribed genus), while confirming the reference to Senecio s.s. of S. ser. Arnicoidei, S. ser. Nemorenses, S. ser. Monticolarum, and S. sect. Senecio. However, the study included no representatives of S. sect. Pinnati, nor of S. ser. Densiserrati, S. ser. Coriaceisquami, S. ser. Stenoglossi, S. ser. Cernui, S. ser. Purpureolobati, S. ser. Malacophylli, S. ser. Subscaposi, and S. ser. Asperifolii; therefore, their disposition remains in doubt. For this reason, Senecio is treated here in a broad sense, although its paraphyly (and perhaps polyphyly) as so circumscribed is acknowledged.
The following three taxa, described or reported from China, are of uncertain identity:
Senecio pelleifolius King ex J. R. Drummond (Bull. Misc. Inform. Kew 1911: 271. 1911). One of us (Jeffrey) notes that this is a name of uncertain application, perhaps an older synonym of Parasenecio palmatisectus.
Senecio campestris (Retzius) Candolle var. oliganthus Franchet (Nouv. Arch. Mus. Hist. Nat., sér. 2, 6: 54. 1883). One of us (Jeffrey) indicates that this belongs to a species of Tephroseris, either T. subdentata or T. kirilowii, and another of us (Nordenstam) concurs.
Senecio lancifer J. R. Drummond (Bull. Misc. Inform. Kew 1911: 270. 1911; Ligularia lancifera (J. R. Drummond) R. C. Srivastava & C. Jeffrey). One of us (Jeffrey) treats this as a Ligularia species, while another of the Asteraceae coauthors (Illarionova) has not seen any material of this species and does not know to which genus it belongs-according to the description, S. lancifer is unlike any species of Ligularia distributed in Xizang.
At least 1,200 species: worldwide (except Antarctica) in the sense adopted here, but generic limits in some areas still uncertain; 65 species (39 endemic) in China.
(Authors: Chen Yilin (陈艺林 Chen Yi-ling); Bertil Nordenstam, Charles Jeffrey, Leszek Vincent)