454 BiCKNELL : Ferns and flowering plants of Nantucket 



the tip of the achene distinctly visible. In P. hydropiperoides the 

 spikes are commonly longer and more slender than in P, opdott' 

 Sana and often interrupted at the base; the ochreolae are longer 

 (2.5-3.5 mm. as against 1.5-2.5 mm.); the flowers on longer 



less spreading pedicels, 3-5 mm. long as against 1.5-3 ^^^ \ ^^ 

 achene of P. opeloiisana is commonly shorter and broader than 

 that of P. hydropiperoides^ more abruptly narrowed to a shorter 

 point, the sides more concave, the angles decidedly more tumid, 

 the surface less shining. Persicaria opeloiisana is more erect In habit 

 than P, hydropiperoides^ which is often decumbent, is less strigillose 

 throughout, commonly with narrower, thicker, paler-green leaves^ 

 less distinctly veined, and characteristically pale beneath. 



In the type specimen oi Persicaria opeloiisana (herb. New York 

 Bot. Garden) and other southern material the flowers are of the same 

 form and color as those of our eastern plant but are rather smaller 

 with smaller and narrower achenes ; the leaves are somewhat 

 thicker and more obscurely veined and more stiffly setulose-stri- 

 gillose along the midrib and margins ; the ochreae are closer, of 

 firmer texture, more strigose, with a longer and stiffer ciliate fringe, 

 5-13 mm. long as against 2-5 mm. long in the northern plant; 

 the ochreolae are also longer-fringed, the hairs 1-5 mm. long 

 whereas in the northern form they are often obsolete and rarely 

 exceed i mm. in length. 



* Persicaria setacea (Baldw.) Small. 



The occurrence of this species on Nantucket is altogether sur- 

 prising, since, although a well-known species of the Southern 

 States, it seems never to have been recorded from north of the 

 Carolinas. It was first collected on Nantucket, Sept 11, 1907, in 

 full flower, growing in the water at the border of Reed Pond, the 

 plants being essentially identical with typical examples from the 

 South Atlantic States. It was again collected, June 17, 1908, 

 along a wet ditch near the head of Millbrook Swamp. Although 

 then only in leaf it appeared notably different from any of our 

 northern species and unmistakable by reason of its large elliptic- 

 lanceolate leaves narrowed to base and apex, at least the upper 

 ones densely short-strigillose over both surfaces, the larger 13 cm. 

 long by 3 cm. wide ; the plants were erect from a prostrate root- 

 ing base and 3-4 dm, high. 



