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. Seeds The 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. The silky white, umbrella-like pappus readily detaches from the fruit when ripe. 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. Distribution York 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. One of the parents Senecio vulgaris is a native to the area 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. Evolution Senecio eboracensis is a hybrid species whose parents are the self-incompatible and promiscuous Sicilian Senecio squalidus (also known as Oxford ragwort) and the self-compatible and tenacious Senecio vulgaris (also known as Common groundsel). Like S. vulgaris, S. eboracensis is self-compatible but shows little or no natural crossing with its parent species and is therefore reproductively isolated, indicating that strong breeding barriers exist between this new hybrid and its parents. It is thought to have resulted from backcrossing of the F1 hybrid of its parents to S. vulgaris. S. vulgaris is native to Britain, while S. squalidus was introduced from Sicily in the early 18th century; 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), now common in Britain, and the allohexaploid S. cambrensis, which according to molecular evidence probably originated independently at least three times in different locations. Morphological and genetic evidence support the status of S. eboracensis as separate