A NEW BRITISH SPECIES OF SENECIO 



By Effie M. Rosser 

 The Manchester Museum, The University, Manchester 



In September 1953 specimens of a large, radiate groundsel were received from 

 Mr. H. E. Green, who had seen similar plants, growing by a roadside in Flintshire, since 

 1948. They could not be assigned to any described European species of Senecio and 

 though they bore some resemblance to the hybrid S. X baxteri Druce (S. squalidus L. X 

 S. vulgaris L.) were more robust, with larger heads and a high percentage of fertile fruits. 



When, in 1954, a chromosome count was made from root tips of plants grown 

 from the Flintshire seed they were found to have the chromosome number 2n = 60; in 

 the same year Professor S. C. Harland and Miss A. Haygarth Jackson produced a similar 

 plant by colchicine treatment of the synthetic hybrid S. squalidus X vulgaris (2n = 30). 

 This evidence confirmed us in the view that the plant should be described as a new 

 species. A description follows. 



Senecio cambrensis Rosser, sp. nov. 



Herba (annua vel) perennis, ad 50 cm. altitudine. Caulis erectus, basi sublignosus 

 saepe parte media dense ramosa et foliosa. Folia inferiora petiolata, superiora sessilia, 

 auriculata; omnia alte et irregulariter pinnatifida, cum lobis distantibus, majoribus liguli- 

 formibus, minoribus lanceolatis, marginibus dentatis vel quandoque lobulatis; folia 

 iuvenescentia tomentosa praesertim subtus, glabrescentia, cum axillis foliorum maturorum 

 lanuginosis. Inflorescentia foliosa, imprimis dense corymbosa postea ramis florentibus 

 longioribus, pedunculis tempore fructescendi longius extensis. Capitula imprimis late 

 cylindracea (ca. 10-0 X 6-0 mm.) tempore florendi flosculorum radii nonnihil campanulata 

 (ca. 12-0 mm. tota diametro); periclinii squamae exteriores minus quam dimidium 

 longitudinis interiorum, omnes apicibus nigris; flosculi radii (8)-13-(15), coroUis flavis, 

 ligulatis latis et curtioribus quam periclinio (ca. 4*8 mm. longitudine et 2*0 mm. latitudine) 

 mox revolutis (saepe ante anthesin flosculorum meiorum disci). Grana pollinis a visu 

 polari (32-8)-33-2-(36-9) fi maxime expansa, pleraque foraminibus quattuor. Cypselae 

 3-0-3-5 mm. longitudine. leviter sulcatae, costis glabris et sulcis hirtellis; pappus albus, 

 sericeus, a fructu facile se disjungens. 



Typus. Roadside near Ffrith, Flintshire, North Wales, 2-10-1954, with Senecio 

 vulgaris L. No. 54102/2 L. W. Frost and E. M. Rosser in Herb. Musei 

 Mancuniensis. 



Isotypi. Herb. Musei Mancuniensis; Herb. Musei Cambrensis; Herb. J. E. Lousley. 



An (annual or) perennial herb, up to 50 cm. high. Stem erect with base somewhat 

 woody, often with the central portion densely branched and leafy. Lower leaves petiolate, 

 upper sessile, auricukte; all deeply and irregularly pinnatifid, with lobes distant, the 

 larger lobes strap-shaped, the smaller lanceolate, with margins of leaves dentate or some- 

 times lobulate; young, growing leaves tomentose, especially below, becoming glabrous, 

 with tufts of cottony hairs in the axils of fully grown leaves. Inflorescence leafy, at first 



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