302 



*** Flowers in axillary or terminal spikes. 



6. P. punctalum Ell. : stem branched ; leaves lanceolate, with pellucid 

 punctures, scabrous on the margin and midrib ; stipules slightly hairy, 

 ciliate ; spikes few-flowered, filiform, at first cernuous ; perianth glandular- 

 punctate; stamens 6 8; styles 2 3. P. Hydropiper Mich. P. hydro- 

 es Pursh. 



Inundated grounds. Can. to Car. Aug., Sept. (). Stem 1 2 feet high, 

 slender, sometimes decumbent. Flowers white, in one or two slender simple 

 spikes. Nut lenticular or triquetrous. Plant very acrid. Water Pepper. 



7. P. mite Pers. : stem erect or ascending ; leaves narrow-lanceolate, 

 acuminate, entire, somewhat hairy ; stipules hairy, with long cilise ; flowers 

 octandrous, in crowded spikes ; styles 3. P. hydropiperoides Mich. 



Ditches and ponds. Can. to Car. July Sept. .Stem 18 inches high. 

 Flowers purplish, in somewhat crowded spikes. Leaves not acrid. Nut trique- 

 trous, purplish-black. Bearded Knotweed. 



8. P. Virginianum Linn. : stem simple ; leaves ovate-lanceolate, acu- 

 minate ; spike terminal, slender, very long ; flowers remote, pentandrous ; 

 perianth unequally 4-parted ; styles 2, P. Distorta Walt. 



Shady woods. Can. to Flor. W. to Miss. July, Aug. 14-. Stem 24 feet 

 high, somewhat angular, hairy near the summit. Leaves large, with hairy 

 stipules. Flowers white or purplish, in a very long naked and somewhat vir- 

 gate spike. Virginian Knotweed. 



9. P. amphibium Linn. : stem nearly erect ; leaves petiolate, oblong- 

 lanceolate, sometimes cordate at base ; flowers in dense terminal spikes, 

 pentandrous ; styles 2. P. coccineum var. terrestre Pursh. 



var. aquaticum Linn. : stem spreading on the surface of water ; leaves 

 ovate-lanceolate, cordate ; spike cylindric-oblong. P. fluitans Eaton. P. 

 coccineum Dig. 



Borders of swamps and ponds. N. S. W. to Miss. July. 9|. Stem 8 12 

 inches long. Flowers large, reddish, in an ovate spike. The var. has the stems 

 long and the leaves broad-cordate and floating ; but it passes into the former. 



Water Knotweed. 



10. P. PennsylvanicumLinn. : stem erect, with tumid joints ; leaves lan- 

 ceolate, slightly hairy, petioled ; stipules smooth and naked ; spikes ob- 

 long, crowded, on glandular-hispid peduncles ; flowers mostly octandrous ; 

 styles 2. 



Margins of ponds and ditches. N. Y. to Car. W. to Miss. July, Sept. 

 CD.- Stem 2 4 feet high, geniculate, branched above. Flowers large, reddish, 

 in numerous crowded spikes. Stamens often 6. Pennsylvanian Knotweed. 



1 1. P. Persicaria Linn. : stem erect ; leaves lanceolate ; stipules trun- 

 cate, ciliate ; spikes dense, ovate-oblong, erect, on smooth peduncles ; flow- 

 ers hexandrous ; styles 2. P. lapathifoliiim Linn. 



Waste places. Can. to Car. July, Aug. (p. Stem 12 18 inches high, 

 erect or decumbent, branched, smooth, often purplish. Leaves on short petioles, 

 the upper surface usually marked with a dark-colored spot. Flowers reddish, 

 in erect oblong terminal spikes. Indies' Thumb. 



12. P. orientate Linn. : stem erect, paniculately branched, hirsute ; 

 leaves very large, petioled, ovate, acuminate, minutely pubescent ; stipules 

 hairy, salverform ; spikes terminal, dense, nodding, on hairy peduncles ; 

 flowers heptandrous ; styles *2. 



