1921] Fernald & Weatherby, — Equisetum fluviatile or E. limosum 43 



The 2-6 bristles perfectly smooth or rarely slightly roughened, 

 0.5-2 mm. long, mostly shorter than the chestnut-brown achene. — 

 Maine: border of salt-marsh, Back River Creek, Woolwich, Sept. 

 15, 1916, Fernald & Long, no. 12830; tidal mud-flats of the Cathance 

 River, Bowdoinham, Sept. 14 & 19, 1916. Fernald & Long, no. 12829; 

 Brunswick, Aug. 6, 1894, C. A. Davis; muddy bank of the Andros- 

 coggin River, Brunswick, Sept. 15, 1904, Kate Furbish; tidal flats 

 of the Cathance River at Bowdoinham and at its mouth in Merry- 

 meeting Bay, Aug. 25-Sept. 2, 1920, Fassett (type in Gray Herb.). 



Harvard University. 



EQUISETUM FLUVIATILE OR E. LIMOSUM? 

 M. L. Fernald and C. A. Weatherby. 



For nearly fifty years before the publication, in 1893, of the List of 

 Pteridophyta and Spermatophyta of Northeastern North America, the 

 common horsetail of our marshes and river-shores was universally 

 known to American botanists as Equisetum limosum L. In that 

 work, the first attempt to apply the provisions of the American Code, 

 the name E. fluviatile was substituted. This change was made be- 

 cause the species, as now and for more than a century understood, 

 includes both E. limosum and E. fluviatile of Linnaeus and of the two 

 names, published on the same page of the Species Plantarum, the 

 latter has priority of position and had to be taken up under Canon 

 13 of the American Code. A. A. Eaton adopted it in his treatment 

 of the North American Equiseta in the Fern Bulletin and in the 

 seventh edition of Gray's Manual; and it is now nearly as generally 

 used in America as was its predecessor twenty years ago. In Europe, 

 however, the great majority of authors have retained E. limosum. 

 This circumstance and the further fact that the International Rules 

 do not admit priority of position in cases where two groups of the 

 same rank, published at the same time, are united, but require the 

 retention of that one of the two names chosen by the author who 

 first suggests the union, raise the question whether, after all, E. 

 fluviatile is the correct name. 



In order to answer this question satisfactorily, it is necessary to 

 consider in some detail the nomenclatorial history of the species. 

 E. fluviatile first appears in the Flora Lapponica, 310 (1737). Its 

 identity is fixed by the existence in Linnaeus' herbarium of a speci- 



