Senecio

Senecio is a genus of flowering plants in the daisy family (Asteraceae) that includes ragworts and groundsels.

Variously circumscribed taxonomically, the genus Senecio is one of the largest genera of flowering plants.

Morphology
The flower heads are normally rayed with the heads borne in branched clusters, and usually completely yellow, but green, purple, white and blue flowers are known as well.

In its current circumscription, the genus contains species that are annual or perennial herbs, shrubs, small trees, aquatics or climbers. The only species which are trees are the species formerly belonging to Robinsonia occurring on the Juan Fernández Islands.

Chemistry
Pyrrolizidine alkaloids are found in all Senecio species. These alkaloids serve as a natural biocides to deter or even kill animals that would eat them. Livestock generally do not find them palatable. Senecio species are used as food plants by the larvae of some Lepidoptera species that have developed tolerance for these alkaloids.

Taxonomy
The traditional circumscription of Senecio is artificial, being polyphyletic, even in its new circumscription which is based on genetic data. Despite the separation of many species into other genera, the genus still contains c. 1,250 species and is one of the largest genera of flowering plants.

As no morphological synapomorphies are known to determine which species belong to the genus or not, no exact species number is known. The genus has an almost worldwide distribution and evolved in the mid- to late Miocene.

Phylogeny
Many genera and the whole tribe are in need of revision. Many species currently placed in the genus need to be transferred to other or new genera, and others have been retransferred to Senecio. In its new delimitation the genus is still not monophyletic.

Genera that have been included are the following:
 * Aetheolaena
 * Culcitum
 * Hasteola
 * Iocenes B. Nord.
 * Lasiocephalus Willd. ex Schltdl.
 * Robinsonia

Synonyms
The following genera contain species that are or have been included within Senecio.
 * Antillanthus B. Nord.
 * Barkleyanthus H. Rob. & Brettell
 * Brachyglottis J. R. Forst. & G. Forst.
 * Canariothamnus B. Nord.
 * Curio P.V. Heath
 * Dauresia B. Nord. & Pelser
 * Dendrophorbium C. Jeffrey
 * Dendrosenecio (Hauman ex Hedberg) B. Nord. - Giant groundsels occurring in the high altitude areas of East Africa
 * Dorobaea Cass.
 * Dresslerothamnus H. Rob.
 * Elekmania B. Nord.
 * Herreranthus B. Nord.
 * Hubertia Bory
 * Jacobaea Mill.Leonis B. Nord.
 * Ligularia
 * Lundinia B. Nord.
 * Mesogramma DC.
 * Monticalia C. Jeffrey
 * Nelsonianthus H. Rob. & Brettell
 * Nesampelos B. Nord., nom. inval.
 * Oldfeltia B. Nord. & Lundin
 * Packera Á. Löve & D. Löve
 * Pentacalia Cass.
 * Pippenalia McVaugh
 * Pittocaulon H. Rob. & Brettell
 * Pojarkovia Askerova
 * Psacaliopsis H. Rob. & Brettell
 * Pseudogynoxys (Greenm.) Cabrera
 * Pseudojacobaea (Hook. f.) R. Mathur
 * Roldana La Llave
 * Sinosenecio B. Nord.
 * Synotis (C. B. Clarke) C. Jeffrey & Y. L. Chen
 * Telanthophora H. Rob. & Brettell
 * Tephroseris (Rchb.) Rchb.
 * Vendredia Baill.
 * Zemisia B. Nord.

Etymology
The scientific name, Senecio, means "old man".

Selected species

 * Senecio ampullaceus — Texas ragwort, Texas squaw-weed, Texas groundsel, clasping-leaf groundsel
 * Senecio angulatus L.f. — creeping groundsel
 * Senecio antisanae
 * Senecio arborescens
 * Senecio barbertonicus Klatt — succulent bush senecio
 * Senecio bigelovii — nodding groundsel
 * Senecio bosniacus G. Beck — Bosnian ragwort
 * Senecio brasiliensis (Spreng.) Less. — flor-das-almas
 * Senecio candicans — angel wings
 * Senecio cambrensis — Welsh groundsel, Welsh ragwort
 * Senecio crassissimus
 * Senecio elegans — purple groundsel
 * Senecio falklandicus
 * Senecio flaccidus Less. — Douglas senecio, threadleaf groundsel, threadleaf ragwort
 * Senecio gallicus Chaix — French groundsel
 * Senecio glaucus L. — Jaffa groundsel
 * Senecio howeanus
 * Senecio inaequidens — South African ragwort
 * Senecio iscoensis — Hieron.
 * Senecio keniophytum
 * Senecio lamarckianus
 * Senecio leucanthemifolius Poir. — coastal ragwort
 * Senecio madagascariensis — Madagascar ragwort
 * Senecio macroglossus — Natal ivy, wax ivy
 * Senecio neowbsteri Olympic Mountain groundsel
 * Senecio patagonicus
 * Senecio pauciradiatus
 * Senecio pulcher
 * Senecio sanmarcosensis
 * Senecio scandens — climbing Senecio
 * Senecio squalidus — Oxford ragwort
 * Senecio trapezuntinus
 * Senecio triangularis — arrowleaf groundsel
 * Senecio tropaeolifolius — false nasturtium
 * Senecio vaginatus
 * Senecio vernalis — eastern groundsel
 * Senecio viscosus — sticky ragwort
 * Senecio vulgaris — common groundsel, old-man-in-the-spring

Formerly in Senecio 
 * Brachyglottis greyi (as S. greyi)
 * Pericallis × hybrida (as S. cruentus)
 * Rugelia nudicaulis — Rugels ragwort

Distribution
The genus Senecio is distributed almost worldwide. It is one of the few genera occurring in all five regions with a Mediterranean climate. Furthermore, species are found in mountainous regions, including tropical alpine-like areas.