83 



Original g^rticlcs. 



ON POLYGONUM NODOSUM. 

 By W. T. Thiselton Dyer, B.A., B.Sc , 



Henry Trimen, M.B., F.L.S. 



The two species o^ Polygonum, P. Perfticaria, L., and P. lap nthi folium, L., 

 are coiispiciioiisly represented in the late summer vegetation of broken 

 and uncared-for land about London, -by several easily recogin'zed forms. 

 Like the Chenopodiums and Atriplexes that grow with them, they flourish 

 on ground which has been liberally cultivated till laid out for building, 

 but which has not yet become hard and consolidated l)y the alternate 

 action of rain-wash and sun-baking. There are always plenty of spots in 

 the advancing outskirts of the suburbs where these conditions are to b< 

 found, and it is seldom necessary to look far for a place to study Poly' 

 (/OHinns. 



Quite the commonest of the London forms, though perhaps not else- 

 where so frequent, are those which are described in English books under 

 the names of P. nodosum or P. laxum. (See Fl. Middlesex, pp. 243, 244.) 

 They are not perhaps collectively separable from typical P. lupaihi folium, 

 by very satisfactory characters, yet they belong to a type which has been 

 well figured by Curtis, Reichenbach, and Babington, and is thoroughly 

 familiar to Metropolitan botanists, — having a certain characteristic fades 

 which serves the ends of recognition, as well perhaps as anything more 

 definite. Typical P. lapatlii folium has a somewhat ditiuse mode of 

 growth, and dense cylindrical and remote racemes, with perianths and 

 unspotted stems of a dull apple-green colour. The P. nodosum, of authors, 

 on the other hand, is rather erect than diffuse, and has stems usually 

 spotted ; racemes collected into a more or less distinct pyramidal panicle, 

 laxer, and narrower in proportion to their length ; the perianths also are 

 reddish and smaller, and the fruit is, roughly speaking, half the size of that 

 of P. lapathifoUum. It was well known to the ante-Linnsean botanists; 

 the Persicaria latifolia geuiculata caulibns maculatis, D. Rand., which was 

 found "passim circa Londinum " (Bay, Syn. iii. 14.5), belongs to it; and 

 two forms were distinguished by Buddie, and are preserved in his herbarium 

 (Herb. Sloane, vol. cxvii. fol. 20). It was described and figured by Curtis 

 under the name of P. Pensylvanicum var. caule maculato (Flor. Lond. f. 1), 

 by Reichenbach as P. nodosum, Pers. (Iconog. Bot. Cent. V. ic. 689), and 

 finally by Babington as P. laxum,^e\c\\. (E. B. S. 28 22). In each case 

 it seems extremely probable that the plant has been wrongly identified. 

 Curtis probably followed Hudson in referring these glandular Polygonums 

 to P. Pensylvanicum,, L., with which, however, they have little coiuiection. 

 It is less easy to decide its claims to be considered the P. nodosum of 

 Persoon. As, however, the description given by that author of his plant 

 is very short, the whole may be quoted for comparison : — 



* Nodosum, caule elongato maculato ad geuiculas nodoso, vaginis nudis, 

 fol. ovato-lanceolatis, spica ramosa. Hab. In humidis, in ruderatis 

 rarius. Caul. 3-pedalis, unc. 1 crassus. Fol. margine et ad petiolos 

 scabra. An a Persicaria specie diversum? (Syn. Plant, vol. i. p. 440.) 



VOL. IX. [FEBRUARY 1, 1871.] D 



