374 POLYGONACEAE 



6. POLYGONUM L. 



Annual or perennial, often somewhat shrubby herbs, with terete, but usually ridged 

 erect or prostrate stems. Leaves alternate : blades leathery or somewhat fleshy, sometimes 

 with two lateral impressions, articulated to the ocreae. Ocreae lobed when young, at 

 length lacerate, hyaline, never fringed. Inflorescence axillary, consisting of clusters bear- 

 ing normally several flowers at each node throughout the plant or confined to the branches 

 and branchlets. Calyx of 5-6 partially united sepals. Sepals mostly green with white or 

 pink margins, 2 wholly interior, 2 wholly exterior and 1 with one edge exterior and one 

 edge interior, the outer sometimes corrugated in age, but not winged. Stamens varying 

 from 3 to 8, often 5 or 6, included : filaments, at least the inner ones, dilated. Styles 3, 

 usually distinct, sometimes very short. Achenes 3-angled, included or slightly exserted, 

 brown or black, granular or smooth and shining. Endosperm horny. Cotyledons incum- 

 bent. The plants flower in the summer and fall, except in the extreme southern part of 

 our range. Knotweed. Dookweed. Knotgrass. 



Stems branciied at the base, the branches prostrate. 



Achenes exserted, chestnut-colored : calyx ,5-7 mm. broad : sepals petaloid. 1. P. maritimum. 



Achenes included, black or brown : calyx 2-3.5 mm. broad : sepals not petaloid. 



Leaf-blades mostly acute : achenes not pinched at the apex. 2. P. avictilare. 



Leaf-blades mostly obtuse : achenes pinched at the apex. 3. P. littorale. 



Stems erect or ascending, more or less diffusely branched above. 

 Fruits erect on the short stout pedicels. 



Leaf-blades without lateral impressions parallel to the midrib. 

 Styles manifest. 



Leaves persistent : achenes granular and dull. 4. P. erectum. 



Leaves fugacious : achenes smooth and shining. 5. P.camporum. 



Styles wanting or nearly so. 6. P. ramoitissimum. 



Leaf-blades with lateral impressions. ' 7. P. tenve. 



Fruits drooping from the slender refiexed or deflexed pedicels. 8. P. Douglasii. 



1. Polygonum maritimum L. Perennial or sometimes annual, glaucous, somewhat 

 fleshy. Stem branched from the base, the branches prostrate, 2-7 dm. long : leaf-blades 

 ovate, oblong or linear-oblong, 0.5-3 cm. long, generally equalling or exceeding the inter- 

 nodes of the stem and branches, obtuse, revolute, strongly nerved especially beneath, 

 somewhat rugose above: ocreae 0.5-1.5 cm. long, at length lacerate, bright and silvery, 

 becoming brown at the base : clusters with 2 or 3 flowers : pedicels slender, 3-4 mm. long : 

 calyx green about the base, 3 mm. long : sepals obovate, petaloid, rather obtuse, white or 

 pink with a green rib : stamens 8 : achenes 3.5-4 mm. long, ovoid, acute or acuminate, 

 chestnut-colored, smooth and shining or minutely granulai-, conspicuously exserted. 



Along the coast, Maine to Florida and Alabama. Also in Europe. 



2. Polygonum aviculare L. Annual or perennial, glabrous, dull green or bluish 

 green. Stem usually branched from the base, the branches prostrate, 1-6 dm. long : leaf- 

 blades oblong, linear-lanceolate or oblanceolate, 0.5-2 cm. long, usually acute or sometimes 

 rather obtuse, not conspicuously nerved : ocreae 4 mm. long, silvery, becoming lacerate with 

 age : clusters with from 2 to 5 flowers : pedicels slender, 1-2 mm. long : sepals oblong, obtuse, 

 with white or pink borders : stamens 5 -8 : achenes 2.5 mm. long, ovoid, acute, dark 

 brown, rounded at the base, rather pointed at the apex, granular and dull. 



Common throughout North America except the extreme north. Also in Europe and Asia. 



3. Polygonum littorale Link. Annual or perennial, bright green, often glaucous. 

 Stem diffusely branclied from the woody base, the branches prostrate, 3-12 dm. long ; inter- 

 nodes often very short, especially at the ends or bases of branches ; the whole plant some- 

 times dwarfed and reduced to a small, erect state less tlian 1 dm. tall : leaf-blades oblong, 

 oblong-lanceolate or oblanceolate, 0.4-2 cm. long, usually obtuse or sometimes acutish, con- 

 spicuously nerved, often crisped : ocreae 4-5 mm. long, silvery when young, at length 

 lacerate and brownish : clusters often numerous, witli from 2 to 6 flowers : calyx mostly green : 

 sepals oblong, obtuse, with wliite borders, or sometimes red : stamens 8 : achenes 2 2.5 

 mm. long, broadly ovoid, usually somewhat constricted and often conspicuously so below 

 the summit, enlarged and rounded at the base, dark brown, more or less granular, mostly 

 dull, sometimes shining. 



In dry soil, New Brunswick to British Columbia, North Carolina, Illinois and California. Also in 

 Europe. 



4. Polygonum er6ctum L. Annual, stout, green, or at length turning yellowish 

 green. Stem erect, or ascending, with somewhat spreading branches, 2-6 dm. long : leaf- 

 blades oval, oblong or obovate, 1-6 cm. long, obtuse or acutish : ocreae 0.3-1 cm. long. 



