410 Polygon aceae Polygonum 



longest generally 5-7 cm long; flowers not crowded; calyx 

 lobes much longer than the achene, usually pink; pedicels 

 generally exserted 1-2 mm; stamens 8 or fewer. 



Achenes all triangular 16. P. hydropiperoides. 



Achenes both lenticular and triangular. (See excluded species 



no. 201, p. 1043.).... P. Ivydropiperoides var. persicarioides. 



Leaves broadly ovate, acuminate, more than 3 cm wide; spikes stout, 



usually more than 1 cm wide, nodding, deep rose; flowers 3-5 mm 



] on g 17. P. orientale. 



Styles long, stiff, exserted, persistent, deflexed, and hooked at the tip in fruit; 

 spikes very long and slender, rigid, greenish; leaves large-ovate and acumi- 

 nate 18. P. virginianum. 



B. Stems armed with hooked prickles, reclining. 



Leaves hastate; pedicels hispid and often glandular; achenes lenticular 



19. P. arifolium var. lentiforme. 



Leaves sagittate ; pedicels generally glabrous ; achenes triangular 



20. P. sagittatum. 



A. Plants twining; leaves broadly ovate, cordate at the base. 



Calyx not keeled or winged in fruit; achenes dull, minutely longitudinally striate, 



about 3 mm long 21. P. Convolvulus. 



Calyx strongly winged in mature fruit; achenes shining, surface not striate. 



Mature calyx 5-8 mm long; achenes 2.5-3 mm long 22. P. dumetorum. 



Mature calyx 7-12 mm long; achenes mostly 3.5-5 mm long 23. P. scandens. 



1. Polygonum exsertum Small. Map 832. Very local. All of our speci- 

 mens were found in hard, dry soil on the washed slopes of the banks of 

 streams and sloughs. Some were very near the water and only one grew 

 on the top of the bank. Bicknell (Bull. Torrey Bot. Club. 36: 450. 1909.) 

 says : "I am unable to see that P. exsertum is anything more than a semi- 

 viviparous state of Polygonum ramosissimum Michx." My observation is 

 that this character applies to late flowering plants of all of the species of 

 the Section Avicularia which occur in Indiana. On November 14, 1932, 

 I studied in the field several large mats of Polygonum avicukire, and I was 

 able to find only exserted achenes. A study of my herbarium material 

 showed exserted achenes on all of the plants collected late in the fall, some 

 with a few and some with a great number of exserted achenes. Early 

 flowering specimens of Polygonum exsertum show a large number of 

 achenes of the normal form, while plants collected in September usually 

 have few or no normal fruits. 



N. B. to Minn., southw. to N. J. and Mo. 



2. Polygonum erectum L. Map 833. This species has been reported 

 from all parts of the state, and no doubt is generally distributed. Since 

 this section of the genus has been divided, however, some of the reports 

 doubtless belong to other species. Most authors give the habitat as rich 

 soil about dwellings and in waste places. With one exception, all of my 

 specimens were found in moist, open woodland, usually in hard, clay soil. 



Ont. to Alberta, southw. to Ga., Colo., and Tex. 



3. Polygonum monspeliense Thiebaud. ( ^Polygonum aviculare var. 

 rcgrtnni of (I ray, .Man., ed. 7.) .Map 834. My specimens are from barn- 

 yards, waste places, and roadsides. It is local, but no doubt when the 



