112 POLYGON ACEAE. 



9. POLYGONUM L. Knotweed. 



Annual or perennial, terrestrial or aquatic herbs, with 

 alternate entire leaves and naked, ciliate or foliaceous 

 margined sheaths. Flowers usually perfect, often col- 

 ored, variously clustered. Pedicels jointed. Calyx 4-5- 

 parted, usually petaloid, the outer segments slightly 

 larger than the inner ones. Stamens 5-9; filaments 

 glabrous; anthers oblong. Style 2-3-parted or 2-3- 

 cleft; stigmas capitate. Achene lenticular or 3-angled, 

 invested by the persistent calyx. 



Flowers spicate. 



Spikes drooping; stamens 6; achenes 



lenticular. 1. P. lapathifolium. 



Spikes erect; stamens 8; achenes 3- 

 angled. 2. P. hydropiperoides. 



Flowers not in spikes. 



Leaves narrowly lanceolate. 3. P. aviculare. 



Leaves cordate. 4. P. convolvulus. 



L P. lapathifolium L. Stem simple or much branched, erect or 

 ascending, swollen at the nodes, 3-12 dm. high, the peduncles and 

 petioles glandular; leaves lanceolate or oblong-lanceolate, 5-20 cm. 

 long, attenuate to the apex, tapering to the short petiole, ciliate, 

 inconspicuously punctate; sheath cylindric, ribbed or striate; 

 racemes panicled, 2.5-10 cm. long, drooping, narrow, rather dense, 

 calyx pink, white or greenish, 5-parted; stamens 6; style 2-parted 

 to below the middle; achene lenticular, 2 mm. long. (P. nodosum 

 Pers.) 



Occasional along streams. 



2. P. hydropiperoides Michx. Stems rather stout, 3-10 dm. 

 high, erect or decumbent, clothed with short appressed hairs; leaves 

 lanceolate, obtuse; sheath cylindric, loose, ciliate; racemes panicled, 

 terminal, erect, narrow, more or less interrupted, 3-7 cm. long; 

 calyx white or whitish, often conspicuous; stamens 8; style 3-parted 

 to below the middle; achene 3-angled, ovoid or oblong, 2-2,5 mm. 

 long, smooth. 



Frequent along streams, especially toward the coast. 



3. P. aviculare L. Annual or perennial, slender, glabrous, 

 bluish-green; stem prostrate or ascending, simple or much branched, 

 1-6 dm. long; leaves linear to oblanceolate, commonly oblong, 6-18 

 mm. long, nearly sessile; sheath oblique, 2-parted or becoming 

 lacerate; flower clusters axillary, 1-5-flowered; flowers small, short 

 pedicelled; calyx green, its 5 lobes with white or pinkish margins; 

 stamens 5-8; style short, 3-parted to near the base; achene 3-angled, 

 ovoid, 2 mm. long, reticulated. 



A common weed in waste places. 



4. P. convolvulus L. Annual, glabrous, scurfy; stem twining 

 or trailing, branched, 1-10 dm. long; leaves ovate-sagittate, long- 



