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 annualorperennial 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.[3]
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.[4]Senecio species are used as food plants by the larvae of some Lepidoptera species that have developed tolerance for these alkaloids.
The traditional circumscription of Senecio is artificial, being polyphyletic, even in its new circumscription which is based on genetic data.[5][6] 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.[7]
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[5] and evolved in the mid- to late Miocene.[8]
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.[5]
Genera that have been included are the following:[5]
The genus Senecio is distributed almost worldwide.[5] 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.
^Pelser, Pieter B.; Tepe, Eric J.; Kennedy, Aaron H.; Watson, Linda E. (2013-06-10). "The fate of Robinsonia (Asteraceae): sunk in Senecio , but still monophyletic?". Phytotaxa. 5 (1): 31–46. doi:10.11646/phytotaxa.5.1.2. ISSN1179-3163.
^ abcdefPelser, Pieter B.; Nordenstam, Bertil; Kadereit, Joachim W.; Watson, Linda E. (2007). "An ITS Phylogeny of Tribe Senecioneae (Asteraceae) and a New Delimitation of Senecio L". Taxon. 56 (4): 1077. doi:10.2307/25065905. JSTOR25065905.
^Passalacqua, Nicodemo G.; Peruzzi, Lorenzo; Pellegrino, Giuseppe (August 2008). "A Biosystematic Study of the Jacobaea maritima Group (Asteraceae, Senecioneae) in the Central Mediterranean Area". Taxon. 57 (3): 893–906. doi:10.1002/tax.573018. JSTOR27756716.
Cyrille Chatelain; Laurent Gautier; Raoul Palese. "Senecio L."African Flowering Plants Database. Conservatoire et Jardin botaniques de la Ville de Genève. Retrieved 2008-03-06.
Instituto Darwinion. "Asteraceae". Catálogo de las Plantas Vasculares de la República Argentina. II (in Spanish). Universidad de Buenos Aires. p. 255. Archived from the original(PDF) on August 21, 2007. Retrieved 2008-03-06.
Landcare Research. "Senecio L."Flora of New Zealand: Taxa. Landcare Research Allan Herbarium and New Zealand Plant Names Database. Retrieved 2008-04-01.
"Search for:genus:Senecio". Species Information. Calflora — 1700 Shattuck Ave. #198, Berkeley, CA 94709. Retrieved 2008-02-09.
