257 



HYDRILLA VEBTICILLx\TA Gasp. IN ENGLAND. 



By Arthur Bennett, A.L.S. 



(Plate 534.) 



HvDRiLLA verticillata Caspavy in Bot. Zeit. xiv. 899 (185G). 



H. ovallfolia Rich, in Mem. Inst. Par. xii. (1811). 



Udora verticillata Gorski in Eicii. Skizze. v. Lithuan., itc, 127 

 (1830). 



U. lithuanica Besser in Flora 11. Beibl. 12 (1832). 



U. occidentalis Koch, Syn. eel. 1. 669 (1837). 



U. pomeranica Reichb. Icones f. 104 (1845). 



This interesting addition to the British Flora has been found 

 by Mr. W. H. Pearsall in Lake Lancashire, v.-c. 69 b, at Estwaite 

 Water, growing with Naias flexilis — itself an occurrence of 

 note — Elodea canadensis, Potamogeton Sturrockii, P. imsillus 

 and CalUtriche autumnalis. The " Water " where the plant 

 occurs is rich in aquatics, and Mr. Pearsall suggests that 

 this may be due, among other causes, to the number of water- 

 fowl that frequent it — wild ducks, coots, water-hens, &c. — by the 

 score. The English examples seem to be produced from winter 

 buds, the first leaves being opposite, then gradually producing 

 leaves in threes and fives (occasionally fours) at each node ; they 

 are linear-acuminate, pellucid, with small cells on the leaf- 

 margins which can hardly be called serrations, as they seem to 

 be extra-marginal — not as shown in Elodea in English Botany, 

 ed. 3, ix. t. 1446. 



The following description is given by Sir J. D. Hooker {P'lora 

 of British India, v. 659) : — 



" A submerged leafy dioecious herb. Leaves short, 3-4-nately 

 whorled, or the lower opposite. Male floiuers solitary, stoutly 

 pedicelled, in a subglobose sessile muricate spathe ; sepals 3, 

 ovate or obovate, green ; petals 3, oblong or cuneiform ; stamens 3, 

 anthers large, reniform, opening elastically ; pistillode small. 

 Female floivers 1-2, sessile in a tubular 2-toothed spathe ; perianth 

 of the male, but leaflets narrower ; ovary produced beyond the 

 spathe in a filiform beak, 1-celled ; styles 2-3, linear, undivided ; 

 stigmas 3, fimbriate ; ovules anatropous. Fruit subulate, smooth or 

 muricate ; seeds 2-3 oblong, testa shortly produced at each end. 



" Plant forming large masses. Leaves \-^ in., 4-8 in a 

 whorl, with a short sheathing one at the base of each branch 

 and a short pair above this ; linear or oblong-linear, serrulate or 

 entire. Flowers ^-J in. long ; perianth segments very variable. 

 Fruit smooth or sometimes muricate, or (in Ceylon) squarrose 

 with filaments above the middle. The male flowers escape from 

 the sheath when mature, and float to the top of the water." 



I have followed Ascherson and Graebner (Syn. Mitteleur. Fl. 



i. 399) in adopting Caspary's name for the plant. The genus is 



near Elodea and Anacharis, and perhaps all three should be 



included under one. The plant has been found in Europe in 



Journal of Botany. — Vol. 52. [October, 1914.] u 



