POLYGONACEAE. 85 



petioles rather short; panicle 10-12 cm. long, the branches short, leafy- 

 bracted; valves triangular-ovate, slightly toothed, 3-4 mm. long, each bearing 

 a large oblong tubercle; akene broad, 2 mm. long. Wet places, common. 



lis. POLYGONUM. 



Annual or perennial, terrestrial or aquatic herbs, some species 

 woody; stems erect, prostrate, climbing or floating; leaves alter- 

 nate, sessile or petioled, continuous with or jointed to the cylindric 

 funnelform or 2-lobed often lacerate or fringed sheaths; flowers 

 small, perfect, green, white, pink or purple, variously clustered, 

 the clusters terminal or axillary; pedicels jointed, subtended by 

 the sheaths; calyx 4-5-parted or cleft, the outer segments larger 

 than the inner; stamens 3-9; stigmas capitate; akene lenticular 

 or 3-angled (rarely 4-angled) , invested by or exceeding the calyx. 



Stems twining; leaves cordate. P. convolvulus. 



Stems not twining; leaves not cordate. 



Leaves small, jointed on the petioles; slender annuals. 

 Stems not striate; flowers in rather dense spikes with 

 imbricated bracts. 

 Bracts oblong, white-margined. P. polygaloides. 



Bracts lanceolate, green. P. confertiflorum. 



Stems striate; flowers axillary or in loose or inter- 

 rupted spikes. 

 Branches not angled; leaves scarcely reduced 

 upwards. 

 Akenes exserted, smooth, shining; low alpine 



plant. P. minimum. 



Akenes not exserted, dull; introduced usually 



prostrate plant. P. aviculare^ 



Branches angled; leaves decidedly reduced 

 upwards. 

 Flowers bell-shaped, 2-3 mm. long. P. douglasit. 



Flowers funnelform, 3.5-4.5 mm. long. P. majus. 



Leaves comparatively large, not jointed on the petioles. 

 Styles 3, long; flowers in a single dense spike-like 



raceme; root tuberous. P. bistorioides. 



Styles 2-cleft; flowers in dense spikes; roots fibrous. 

 Perennial aquatic or swamp plants. 



Sheaths ciliate on the spreading border. P. hartwrighlii. 



Sheaths not ciliate. 



Leaves elliptic, obtuse or acutish; pe- 

 duncles glabrous. P. amphibium. 

 Leaves lance-ovate, acuminate; peduncles 



hispid. P. emersum. 



Annuals. 



Sheaths ciliate. P. persicaria. 



Sheaths not ciliate. 



Leaves not tomentose beneath. P. lapathifolium. 



Leaves tomentose beneath. P. tomentosum. 



Polygonum convolvulus L. Annual; stems twining or prostrate, 50-100 

 cm. long, glabrous or pubescent, scurfy below; leaves heart-shaped or some- 

 what halberd-shaped, acuminate, 2-6 cm. long, minutely scurfy beneath; 



