Senecio nebrodensis auct., non L. Senecio laciniatus Bertol.[2] Senecio rupestris Waldst. & Kit.[3] Senecio squalidus d'Urv. Senecio squalidus Willd. Senecio squalidus M.Bieb.[4] Jacobaea incisa C. Presl Senecio glaber Ucria Senecio incisus (C. Presl) C. Presl[5]
Senecio squalidus, known as Oxford ragwort,[6] is a flowering plant in the daisy familyAsteraceae. It is a yellow-flowered herbaceous plant, native to mountainous, rocky or volcanic areas, that has managed to find other homes on man-made and natural piles of rocks, war-ruined neighborhoods and even on stone walls. These habitats resemble its well drained natural rocky homeland. The plants have spread via the wind, rail and the activities of botanists. The travels and discriminative tendencies[clarification needed] regarding propagation of this short-lived perennial, biennial, or winter annual make it a good subject for studies of the evolution and ecology of flowering plants.
Description
Like all members of the Asteraceae family, Senecio squalidus has a composite flower head known as a capitulum. What look like single flowers are actually a cluster of florets, each petal or ligule being a flower, or floret, possessing its own stamen and capable of producing the specialized seed of the family Asteraceae, the parachute-like achene.[7]
Oxford Ragwort is a short-lived perennial, a biennial, or a winter annual and grows in a branched straggling form to between 1.5 feet (0.5 m) and 3.3 feet (1 m) depending on conditions. S. squalidus prefers dry, disturbed places, cultivated and waste ground, walls and railway banks,[3][8]
flowering from March[9] to December[8]
and reproduces from seed.[3]
Leaves and stems
S. squalidus leaves are alternate, glossy, almost hairless and variable in form from deeply pinnately lobed to undivided with only the lower leaves being stalked. Stems and leaves resemble those of the common groundsel (Senecio vulgaris)[3][8] with the exception that their lobes are more widely spaced.[10]
Inflorescence
S. squalidus has larger capitula than Senecio jacobaea and a more spreading habit.[9] Yellow capitula of 10-14 petals in loose clusters. They are pollinated by insects. Ray corollas .3 inches (8 mm) to .6 inches (15 mm) long, .08 inches (2 mm) to .16 inches (4 mm) wide.[8]
Oxford ragwort is self-incompatible and needs pollen from other plants with different self-incompatibility alleles;[11]
[12][13] its own flower possess a stigma with characteristics of both the “dry” and “wet” types.[14]
Each pollinated Oxford ragwort floret matures into a bell to cylindrical shaped indehiscent achene, the shallowly ribbed fruit is light brown in colour and .06 inches (1.5 mm) to .12 inches (3 mm) long.[8] Each plant can produce approximately 10,000 fruits during the year.[15]
Mature capitulum
S. squalidus developing capitula.
Leaves and stalks of S. squalidus.
Capitula at different stages of development
As a Senecio and a diploidSenecio squalidus is part of a species group along with S. flavus, S. gallicus, S. glaucus and S. vernalis, which are widespread geographically and interesting for the study of genetic differences in relation to the environment and plant evolution.[16]
History
This Senecio was introduced into Britain via Francisco Cupani and William Sherard in the years of their visit 1700, 1701 and 1702 from Sicily[17]
where it lives as a native on volcanic ash[15] to the Duchess of Beaufort's garden at Badminton. Later a transfer of the genetic material to the Oxford Botanic Garden by the "Horti Praefectus" (the title still given to the head gardener at the Oxford Botanic Garden[18]) Jacob Bobart the Younger before his death in 1719[19] (which is also the same year that Bobart retired as Horti Praefectus[18] and perhaps a good indication of when this species of ragwort and other invasive species might have "escaped" and started to make their home in the greater British Isles). The Sicilian ragwort escaped into the wild and grew in the stonework of Oxford colleges (with the specific mention of the Bodleian Library[9]) and many of the stone walls around the city of Oxford. This gave the plant its common name, "Oxford Ragwort".[20]
Carl Linnaeus first described Senecio squalidus[21] in 1753, although there is a dispute as to whether the material came from the Botanic Garden or from walls in the city; the taxonomy for this species is further complicated by the existence of species with a similar morphology in continental Europe.[19]
James Edward Smith officially identified the escaped Oxford ragwort with its formal name Senecio squalidus in 1800.[19]
The vortex of air following the express train carries the fruits in its wake. I have seen them enter a railway-carriage window near Oxford and remain suspended in the air in the compartment until they found an exit at Tilehurst.
During the 20th century it continued to spread along railway lines and found a liking for waste places and bombed sites after World War II which have a lot in common with the volcanic regions of home.[9]
Recently, this and other Senecio and their differing tastes for self-incompatibility and self-compatibility have been the subject of study for the purposes of understanding the evolution of plant species as the genus finds new homes and pollen partners throughout the world:
The origin of Senecio vulgaris var. hibernicus Syme was determined to be an introgression of Senecio squalidus into Senecio vulgaris subsp vulgaris
The suggestion that S. squalidus is actually a hybrid of two other Sicilian Senecio: S. aethnensis Jan ex DC and S. chrysanthemifoliusPoir.[19]
Distribution
Senecio squalidus grows on scree in mountainous regions of native range,[3] and earned its common name Oxford ragwort for its willingness and ability to grow in similar habitat elsewhere in the world.[19]
^"BSBI List 2007". Botanical Society of Britain and Ireland. Archived from the original(xls) on 2015-01-25. Retrieved 2014-10-17. ((cite web)): Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ ab"Details for Senecio squalidus L."The National Biodiversity Network's Species Dictionary. Natural History Museum, London. 1994-08-12. Retrieved 2008-02-14.
Hollingsworth, Peter; Richard M. Bateman; Richard Gornall (1999). "Monophyly populations and species". Molecular Systematics and Plant Evolution. CRC Press. pp. 504 pages. ISBN0-7484-0908-4. Retrieved 2008-04-23. ((cite book)): External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
"Senecio squalidus". :: Flora of Northern Ireland ::. National Museums and Galleries of Northern Ireland and Environment and Heritage Service. Retrieved 2008-02-14.((cite web)): CS1 maint: extra punctuation (link)