198 Transactions. 



Art. XXI. — On the Distribution of Senecio saxifragoides Hook. /.' 

 and its Relation to Senecio lagop.us Raoul. 



By Professor A. Wall, M.A. 

 Communicated by R. Speight, M.Sc. 



[Read before the Philosophical Institute of Canterbury, 5th December, 1917 ; received by 

 Editors, 31st December, 1917 ; issued separately. 10th June, 1918.] 



Plates XI-XIII. 



1. Introduction. 



(a.) General. 

 The problem to be attacked in this paper is suggested in the following 

 passage from L. Cockayne (" Notes on the Plant Covering of Kennedy's 

 Bush and other Scenic Reserves of the Port Hills," Report on Scenery 

 Preservation, Parliamentary Paper C.~6, 1915) concerning S. saxifragoides : 

 " It also is a most striking plant. Now, an almost identical species, named 

 Senecio lagopus, also occurs on the main mass of Banks Peninsula, which 

 differs from S. saxifragoides merely in the possession of numerous bristles 

 on the leaf, whereas in the latter such are absent. Yet, so far as is known, 

 S. lagopus does not occur on the Port Hills, nor S. saxifragoides on Banks 

 Peninsula proper. If this is truly a fact, the distribution of these two 

 species, each equally well suited to the rock-conditions of the area, is one 

 of the most remarkable cases of plant-distribution in the world." 



The same authority, in his description of his new species, Senecio south- 

 landicus {Trans. N.Z. Inst., vol. 47, p. 118, 1915), further says, " The 

 species is, indeed, far more distinct from S. bellidioides and S. lagopus than 

 are these from one another. The classification of the whole series, includ- 

 ing those already mentioned, together with S. saxifragoides Hook. f. and 

 S. Haastii Hook, f., is in a most unsatisfactory position. Specimens are 

 constantly coming to me from various correspondents which it is impossible 

 to place with any degree of satisfaction. There are undoubtedly a number 

 of well-marked forms, which demand, at the least, varietal names. Even 

 one fixed character may serve quite well as a specific mark. This is illus- 

 trated in the case of S. saxifragoides and S. lagopus (the type from Akaroa), 

 where the presence of numerous bristles, or their absence, on the upper 

 surface of the leaf is the sole distinguishing character, so that, so far as 

 large plants of the two are concerned, if this character were not present no 

 one could consider them in any degree different." 



In this paper attention has been directed to these two species solely as 

 they occur on Banks Peninsula. 



Banks Peninsula is situated in lat. 43° 32' S. and long. 175° 30' E., and 

 forms a rough elliptical salient on the east coast of the South Island of New 

 Zealand. Its diameter in a N.W.-S.E. direction is about twenty-five miles, 

 and its breadth at right angles thereto about eighteen miles. Some forty 

 miles to the westward stretches the main chain of the Southern Alps, from 

 which the peninsula is separated by the gently inclined expanse of the 

 Canterbury Plains, so that it is almost as completely isolated as regards 

 the distribution of subalpine vegetation as if it had been separated from 

 the mountain region by the sea. 



The oldest rocks within its limits consist of Trias-Jura sedimentaries 

 overlain in places by a thin veneer of Cretaceous rhyolites, but the main 



