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dDriighuiI %.xiultB. 



IS TPIERE A SECOND EUROPEAN HYDROCOTYLE? 

 By Berthold Seemann, Ph.D., F.L.S. 



In publishing my revision of the Hederacea I was compelled to omit 

 IJydrocotyle, as several species of that genus had been so insufficiently 

 described, that nothing but an inspection of authentic specimens could 

 set the matter to rights. One; of these was the European //. pleiantha, 

 Cesati, in Linnsea, xi. p. 313. From the description it would seem 

 to be a form intermediate between IT. vulgaris, L., and II. verticillata, 

 Thunb. ; and as none of the specimens of these two species which I 

 had an opportunity of examining furnished any characters which would 

 obliterate the boundary between the two, I was naturally anxious to 

 see authentic specimens of //. pleiantha. Professor Caruel, of Flo- 

 rence, the distinguished author of the ' Flora of Tuscany,' was good 

 enough to send me specimens which he believed to be Cesati's //. 

 pleiantha ; but all of them proved to be mere forms of H. vulgaris. 

 In April last I was fortunate enough to obtain from Baron V. Cesati 

 himself, who is now Director of the Botanic Gardens at Naples, au 

 authentic specimen of his //. pleiantha ; and, in sending it to me, he 

 pointed out that in the diagnosis of the leaves the words " minutissinie 

 denticulati" should be substituted for " perfine denticulati." Tliis 

 specimen and the diagnosis published establish the identity of //. 

 vulgaris, L., and H. pleiantha, Ces., and also show that there is, as 

 far as //. pleiantha is concerned, no transition between the European 

 II. vulgaris and the American, African, and Australasian H. verticillala. 



I have gone closely into tlie question of identity between H. veriicil- 

 lata and H. vulgaris, and have examined every specimen contained in 

 the public herbaria of this country. The conclusion arrived at is that, 

 though the two species are close together, they do not coexist in the 

 same geographical area, and have several distinguishing characters. 

 II. vulgaris has tlie petioles generally hairy towards the top, the leaves 

 never more than ^-nerved, the fruit generally emarginate at base, and, 

 when approaching maturity, covered with purplish or blood-red 

 blotches and dots. //. verticillata has leaves always 11-ncrved, gla- 



voL. VIII. [august 1; 1870.] 8 



