2 to 3 times as long as the flowers but only slightly if at all broadened or white- 

 margined; perianth (1.5-) 2-2.5 mm. long, connate scarcely one third the length, 

 the 5 lobes subequal or the outer 3 the largest, slightly cucullate-keeled, with 

 a green midstripe and whitish or pinkish borders; stamens 8, the 5 outer ones 

 with linear filaments and abortive or no anthers, the 3 inner filaments greatly 

 dilated at base and anther-bearing; stigmas 3, subsessile; achene triquetrous, 

 1.5-2 mm. long, usually light-yellow to greenish-brown, shining and smooth to 

 obscurely striate, sometimes dark-brown, dull and strongly striate lengthwise 

 (both types of achene often on the same plant); style very short, connate about 

 half the length. 



Meadows, wet banks of lakes and vernal pools to dry subalpine slopes in Ariz. 

 (Coconino Co.), June-Oct.; Mont, to B.C., s. to Colo., Ariz, and Calif. 



9. Polygonum aviculare L., sens. lat. Knotweed, wiregrass. Fig. 404. 



Taprooted annual or very weak perennial, very diverse in habit, either with 

 an upright mainstem and ascending branches (when growing among dense herba- 

 ceous vegetation) or usually prostrate and rooting at the very numerous nodes 

 (when on flat bare ground); leaves few to numerous, sparse to crowded; blades 

 caducous or long-persistent, linear to usually narrowly oblong or narrowly 

 elliptic, (2-) 3-15 (-25) mm. long, green, flat, without conspicuous nervation; 

 flowers solitary or in 2's or 3's at some of the nodes, crowded or not; pedicels 

 filiform, much shorter than the ocreae so that the flower and fruit are always 

 erect; sepals 5 (calyx never opening, perhaps indicating cleistogamy), 3 of them 

 exterior over the angles of the achene and 2 inner ones over 2 of the achene faces. 



In marshes and mud on edge of ponds, lakes and streams, wet meadows, flood- 

 lands and edge of tidal salt marshes, widespread but local nearly throughout Tex. 

 (except extreme s.), Okla. (Rogers and Osage cos.), N. M. (Lincoln, Grant, Colfax, 

 Otero, San Miguel, Taos and Rio Arriba cos.) and Ariz. (Navajo and Coconino, 

 s. to Cochise and Pima cos.), May-Nov.; very widespread in temp, regions, per- 

 haps originally nat. to Eur. 



On the basis of achene and caixy characters 3 species in the P. aviculare aggre- 

 gate may be differentiated as follows: (1) plants having achenes with 2 convex 

 and 1 narrowly concave side are referred to P. arenastrum Bor.; achenes mildly 

 striated, reddish-brown, about 2 mm. long; the persistent calyx covering the 

 achene is divided for about half its length; (2) plants designated as P. buxiforme 

 Small have reddish-brown striated achenes 2-2.5 mm. long, cordate in shape, with 

 1 broad flat face and 2 more or less equal concave sides; the persistent perianth 

 is divided for about two thirds its length and is characterized by having lateral 

 papery margins or wings; (3) achenes of P. aviculare (sens, str.) are typically 

 coarsely striated, dull, 2.5-3 mm. long and narrower, and less heart-shaped than 

 those of P. buxiforme; the persistent perianth completely covers the achene, is 

 divided almost to the base and lacks the lateral papery margins characteristic of 

 P. buxiforme. 



10. Polygonum Douglasii Greene. 



Simple to freely branched, erect to strongly ascending annual 1-4 (-5) dm. 

 tall; leaves numerous but not strongly overlapping, linear to narrowly oblong 

 (sometimes more nearly lanceolate or oblanceolate), usually 2-4 cm. long, rarely 

 as much as one fifth as broad, sessile or subsessile, jointed at the base, rather 

 abruptly reduced to the bracts above; stipules short-sheathing, 5-12 mm. long, 

 lacerate; racemes elongate, loose, with (1) 2 to 4 flowers per node; pedicels 1-4 

 mm. long, reflexed by (or shortly after) anthesis; upper bracts much shorter 

 than the flowers; perianth 2.5-3.5 (-4) mm. long, distinct nearly to the base, the 

 5 segments greenish witn white or reddish margins; styles 3, distinct nearly to 



816 



