Senecio eboracensis

Senecio eboracensis
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Asterales
Family:	Asteraceae
Tribe:	Senecioneae
Genus:	Senecio
Species:	S. eboracensis
Binomial name
Senecio eboracensis Abbott & Lowe[1]
Range of Senecio eboracensis in Great Britain.

Senecio eboracensis, the York groundsel or York radiate groundsel, is a self-pollinating hybrid species of ragwort^[2] and one of only six new plants to be discovered in either the United Kingdom or North America in the last 100 years.^[3] It was discovered in 1979 in York, England growing next to a parking lot and formally described in 2003. Like many of the Senecio genus it can be found growing in urban habitats, such as disturbed earth and pavement cracks and this particular species only in York and between a railway and a parking lot.^[2][4]

Description

York radiate groundsel is a deciduous annual plant that sets its seed within the 3 months^[3] that it takes this plant to mature from germination to the upwards of 16 inches (41 cm) high adult plant. With pretty yellow daisy-like flowers from its Sicilian parent (S. squalidus) but also with the less-promiscuous habits of its native parent (S. vulgaris); this member of the Senecio genus is morphologically distinct from related species.^[2]

Leaf shapes of S. eboracensis

Leaves and stems

S. eboraccensis have large many lobed leaves divided into slender segments, the clefts not reaching the midrib. The stems are mostly erect to ascending with an occasional horizontal base section up to 2 inches (5 cm) with 'adventitious roots' at base. The upper and lower leaves petiolate and lobes appearing at quarter whole leaf lengths along the midrib. The upper leaves are generally more deeply lobed and in lobed pairs. Leaves on plants grown in fertile soils or in greenhouses can be much more luxurious and more highly dissected (or more finely divided into slender segments) up to 7 inches (18 cm) x 3.5 inches (9 cm) with lobes appearing at fifth whole leaf lengths along the midrib. The plants tip is usually acute with a very small tooth. Leaf edges throughout are dentate or sometimes divided into lobes.^[2]

Flowers

York groundsel has showy flower-heads especially when compared to its Common ragwort parent. The flower-head, found at the tips of the plants (apical) appearing in clusters (an inflorescence) usually consists of three to seven florets in a grouped corymb; at first dense and leafy but eventually less dense with peduncles 5 to 20 millimeters (0.2 to 0.8 in) which get longer when fruiting (up to 25 mm (1 in)). The flower-head is broadly cylindrical 10×4 millimeters (0.4×0.16 in), becoming slightly bell shaped) when the bright yellow ray florets open. Involucral bracts sparse (4-8), elongated (3.5–4 mm), usually without black tips. The floret ligules are narrow and long 5 to 7 millimeters (0.2 to 0.24 in) long and 1.5 millimeters (0.06 in) wide), occasionally becoming revolute. Like other Senecios, the 10-30 papilla occur stigmatically into pericarp; each usually with four-pored pollen, the grains in polar view 30-35 micrometers when fully expanded.^[2]

Seeds

The umbrella-like achenes can be 2.5 to 3.5 millimeters (0.1 to 0.15 in) long, are straight and shallowly grooved; with hairless smooth ribs while the grooves are covered with hairs. Silky white pappus which readily detach from the fruit when ripe.^[2]

Name

The word Eboracum, the classical name of York, was chosen in the year 2000 to describe this tetraploid hybrid derivative informally named 'York radiate groundsel' at the time a formal description was made.^[2]

Distribution

This groundsel occurs on disturbed ground, car park perimeters, pavement cracks and other urban/industrial sites; specifically in disturbed areas near to the railways in York, England.^[2]

One of the parents Senecio vulgaris is a native to the area^[5] while the other parent Senecio squalidus was introduced from Mount Etna in Sicily in 1690 to the Oxford Botanic Garden in Oxford, England and was soon spreading happily along the railways and throughout the country.^[6]

Evolution

A newcomer to the plant world, York groundsel has been used as an example to support macroevolution. The refusal of S. eboracensis to breed back to its parents is the main point of contention between the rival parties.

The science of this plant is that it is a hybrid species whose parents are the self-incompatible and promiscuous Sicilian Senecio squalidus (also known as Oxford ragwort)^[6] and the self-compatible and tenacious Senecio vulgaris (also known as Common groundsel). Like S. vulgaris, S. eboracensis is self-compatible, however, it shows little or no natural crossing with its parent species, and is therefore reproductively isolated, indicating that strong breed barriers exist between this new hybrid and its parents.^[4] It is thought to have resulted from a backcrossing of the F1 hybrid of its parents to S. vulgaris.^[2] S. vulgaris is native to Britain, while S. squalidus was introduced from Sicily in the early 18th century;^[2] therefore, S. eboracensis has speciated from those two species within the last 300 years.

Other hybrids descended from the same two parents are known. Some are infertile, such as S. x baxteri. Other fertile hybrids are also known, including S. vulgaris var. hibernicus (which has been accepted as a synonym for S. vulgaris^[7]), now common in Britain, and the allohexaploid S. cambrensis, which according to molecular evidence probably originated independently at least three times in different locations.^[2] Morphological and genetic evidence support the status of S. eboracensis as separate from other known hybrids.^[2][4]

See also

• Common Cordgrass
• Welsh groundsel
• Tragopogon miscellus
• Tragopogon mirus
• Raphanus sativus x Brassica rapa

References

External links

Data related to Senecio eboracensis at Wikispecies Media related to Senecio eboracensis at Wikimedia Commons Media related to Tyria jacobaeae at Wikimedia Commons

• Lowe, A.J.; Abbott, R.J. (May 2004). "FIGURE 2, Reproductive isolation of a new hybrid species, Senecio eboracensis Abbott & Lowe (Asteraceae)". Heredity 92 (5): pp. 386–395. doi:10.1038/sj.hdy.6800432. PMID 15014422. Retrieved 2008-02-14. 
• Arnold, Michael L. (2006). Evolution Through Genetic Exchange. Oxford University Press. pp. 47 of 272 pages. ISBN 0-19-857006-6. Retrieved 2008-02-14. 
• "Taxa covered by the Threatened Plants Database" (PDF). Botanical Studies of the British Isles. 2006-03-20. Retrieved 2008-02-14. 
• Adrian C Brennan, Stephen A Harris, and Simon J Hiscock, Department of Plant Sciences; Adrian C Brennan; Stephen A Harris; Simon J Hiscock (2003-06-29). "The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae): avoidance of mating constraints imposed by low S-allele number.". Philosophical Transactions of the Royal Society (Carlton House Terrace, London, England: Royal Society) 358 (1434): 1047–1050. doi:10.1098/rstb.2003.1300. PMC 1693209. PMID 12831471. Retrieved 2008-02-14. 

Further reading

• Abbot, R.J.; Lowe, A.J. (2003). "A new British species, Senecio eboracensis (Asteraceae), another hybrid derivative of S. vulgaris L. and S. squalidae L." (PDF). Watsonia 24: pp. 375–388. Retrieved 2008-02-12.