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 dry-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 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 family Asteraceae, 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] It flowers 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 flowers 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]
Carl Linnaeus first described Senecio squalidus[20] 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.[18]
James Edward Smith officially identified the escaped Oxford ragwort with its formal name Senecio squalidus in 1800.[18]
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 its home.[9]
Recently, this and other Senecio species 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.[18]
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.[18]
^ abcdPeter Llewellyn (23 August 2004). "Senecio squalidus Oxford ragwort". Wild Flowers of the British Isles. Wild Flower Society. Retrieved 12 February 2008.
^ ab"Details for Senecio squalidus L."The National Biodiversity Network's Species Dictionary. Natural History Museum, London. 12 August 1994. Retrieved 14 February 2008.
"Senecio squalidus". Flora of Northern Ireland. National Museums and Galleries of Northern Ireland and Environment and Heritage Service. Retrieved 14 February 2008.
