1-t J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



important distinguishing marks employable to the systematist. Especially the stem- 

 anatomy is rather uniform. 



Five species are known which should be divided in tvvo subsections. 



Subsectio i. Filiformes Hagstr. 

 Fruetus rostro brevissimo verrueseformi. 



P. filiforillis Persoon, Syn. plant. I. (1805), 152. 



P. setaceus Schum., Enum. plant. Ssell. I, 1801, 51 (non L.). — P. borealis 

 Rafin. in Med. Reposit. 1808, 354? — P. maritimus Pohl, Tent. Fl. Bohem. I, 1810, 

 159 ex Graebner, Potamog. in Engler, Pflanzenr. IV, 11, 1907, 126. 1 — P. fascicula- 

 tus Wolfg. in J. A. et J. H. Schultes, Mänt. in vol. III syst. veg. 1827, 364—365. 

 — P. marinus L. ex Fr., Novitias Fl. suec. 1828, 54. — P. salinus Schur, Phytogr. 

 Fragm. CII, in Österr. Bot. Zeitschr. n. 9, 1870, 280 (nomen solum). — P. capilla- 

 ceus Moerck, Herb. Mus. Brit. 1821 ex Ar. Benn. in Journ. of Bot. 1890, 301 (nomen 

 solum). — Figs. 3 and 4. 



The expression of P. Bocconi, that Linné is said to have used, though not in the 

 Öländska och Gotl. Resan 1745, 221, must not be understood as a species-name but 

 only as a reference to the Fig. 5. tab. 20 in Boccone, Icones et descr. etc. and is 

 an abbreviation instead of »Potamogeton pusillum fluitans Bocconi". 



By the authority of Prof. E. Fries the name marinus has been cmployed quite 

 up to our days (Hartman, Handb. 1879; Richtér, Pl. eur. 1890). Before Fries it 

 was applied to some forms of P. pectinatus (Linné, Roth, Sciiumacher, Flora Da- 

 nica, Lamarck & De Candolle, Smith, Hartman, Wahlenberg and others) or to 

 forms belonging both to pectinatus and filiformis (Allionius, Fl. pedem. ex s} T non.). 



P. filiformis has often been mixed up with P. pectinatus and considered as a 

 variety or subspecies of it (Hooker, Stud. fl. Brit. Isl. 1878). Even as late as in 

 1894 K. Schumann hesitatingly designates it as a distinct species (Flora brasil. III, 

 3, 696) and P. Graebner comprehends pectinatus, vaginatus, amblyophyllus, filiformis 

 and pamiricus to a species collectiva »P. pectinatus* (Potamog. 1907, 121); so still in 

 the Synopsis mitteleur. Fl. 1913, 538. G. Fischer certainly soparates it from P, 

 pectinatus, but regards it together with P. juncifolius as subspecies of a collective 

 species >marinus autt. » (Die bayer. Potamog. 1907, 130). 



No doubt /'. filiformis is an independent species and well distinguished from 

 /'. pectinatus. Beside the differences mentioned by S. Almquist, G. Fischer and 

 others, the most important of which, of course, pertain to the style and stigma (fig. 

 3, A), the fruit, the small perianth-leaves and the infloreseence, the dark-bordered 

 connatc Bheaths (fig. 3, B) and obtuse leaves (fig. 3, F-II), wc must also observc 

 fchat the pollengrains are smaller and the hybrids of the fcwo species always Bterile. 



1 Vci ii is nncertaio if /'. filiformis is lien' concerned. The name maj baye been adopted after Plu- 

 iii description in Ålmagestum botanicum 1696; V. maritimum ratnosissimum etc. or ii may simply be a 



liii-jniiit. 



