FLORA OF THE DISTRICT OF COLUMBIA. 149 



1. XRESINE P. Br. 



1. Iresine rhizomatosa Stand ley. 



Known witliin our region only from Plummers Island, the type locality. South- 

 eastern U, S. 



The species has usually been confused with I. celosia L. (/. paniculata Kuntze; 7. 



celosioides L.) 



2. ACNIDA L. 



I. Acnida cannabina L. Water hemp. 



Waste or swampy ground along the Potomac about Washington and Alexandria; 

 rare. Aug.-Oct. N. H. to N. C. 



3. AMARANTHUS L. 



Plants with long stout spines in the leaf axils 1. A. spinosus. 



Plants without spines. 

 Flower clusters all in the axils of the leaves, mostly shorter than the petioles. 

 Plants erect; seed about 0.8 mm. broad; bracts much longer than the sepals, 



with long slender tips 2. A. graecizans. 



Plants prostrate; seed about 1.5 mm. broad; bracts about as long as the sepals, 



with short tips 3. A. blitoides. 



Flower clusters in long spikes arranged in panicles. 



Flowers bright purplish red ; sepals shorter than the fruit 4. A. cruentus. 



Flowers green or the spikes slightly tinged with red; sepals equaling or longer 

 than the fruit. 

 Sepals acute, the flower spikes slender, green or yellowish green; plants gla- 

 brous or nearly so 5. A. hybridus. 



Sepals very obtuse, often notched at the apex, the spikes very stout, whitish; 

 plants very hairy about the inflorescence 6. A. retroflexus. 



1. Amaranthus spinosus L. Spiny amaranth. 

 Waste and cultivated ground. July-Oct. Native of tropical Amer. ; widely 



naturalized in the eastern U. S. 



2. Amaranthus graecizans L. Tumbleweed. 

 Waste and cultivated ground. July-Oct. Throughout the U. S. and southern 



Canada. (A. alhus L.) 



3. Amaranthus blitoides S. Wats. 



Waste ground, especially along railroads; rare. Native of the southwestern U. S. 

 but now adventive in many places eastward. 



4. Amaranthus cruentus L. 



Waste ground; infrequent. Native habitat not known but probably tropical 

 Amer., the plant sometimes cultivated and escaping. {A. paniculatus L.) 

 6. Amaranthus hybridus L. Common amaranth or pigweed. 



An abundant weed in waste and cultivated ground. July-Oct. Widely dispersed 

 in N. Amer., adventive northward. {A. retrofiexus of Ward's Flora.) 



6. Amaranthus retrofiexus L. 

 Waste and cultivated ground; infrequent. July-Oct. Nearly thi-oughout the U.^ 



5. and southern Can. 



48. ALLIONIACEAE. Four-o'clock Family. 



1. ALLIONIA L. 



1. AUionia nyctaginea Michx. Umbrellawort. 



Along the railway embankment at Chevy Chase Lake, well established. May, 1916 



{Maxon & Standley). Native of the western U. S.; often adventive eastward. {Oxyb 

 aphus nydaginfus Sweet.) 



