FLORA OF THE DISTRICT OF COLUMBIA. 231 



128. ASCLEPIADACEAE. Milkweed Family. 



Plants with twining stems, the leaves heart-shaped, long-petioled. 

 Corolla lobes spreading, reddish brown or greenish; crown a continuous ring or cup 

 the 5 fleshy divisions more or less fused together; pod smooth and wing 



angled or roughened with warty projections 1. VINCETOXICUM. 



Corolla lobes erect, white; crown of 5 thin flat awned processes; pod smooth, not 



strongly angled 2. GONOLOBTTS. 



Plants erect or decumbent, never with twining stems, the leaves sessile or short- 

 petioled. 

 Leaves mainly alternate; hoods of the crown without horns or other included out- 

 growths; pod smooth 3. ACERATES. 



Leaves mainly opposite or whorled; crown of 5 hoods, each covering a distinct 

 curved horn-shaped outgrowth; pod smooth or warty 4. ASCLEPIAS. 



1. VINCETOXICUM Walt. 



Crown a low wavy ring; pods smooth, angled; seeds very dark brown. 



1. V. suberosum. 

 Crown cup-shaped; pods warty, not angled; seeds reddish brown. 

 Buds conical; corolla lobes linear to strap-shaped, about 15 mm. long; racemes 



several to many-flowered 2. V. obliquum. 



Buds elongate-ovoid; corolla lobes elliptic to linear-oblong, about 10 mm. long; 

 racemes few-flowered 3. V. carolinense. 



1. Vincetoxicum suberosum (L.) Britton. Angle-pod. 

 Open thickets along the Potomac near Fort Washington (C. P. Smith). July; fr. 



Nov. Va. to Fla. (Gonolobus suberosus R. Br.) 



This is the only species of this region to which the name "angle-pod " is really appli- 

 cable. The seeds are much darker brown than in any other milkweed of our region. 



2. Vincetoxicum obliquum (Jacq.) Britton. 



Frequent in thickets near the Potomac. June; fr. Oct.-Nov. Southeastern 

 U. S. {Gonolobus obliquus R. Br.) 



The seeds are the shade of reddish brown common to most milkweeds of this 

 region. 



3. Vincetoxicum carolinense (Jacq.) Britton. 



Occasional in thickets south and east of Congress Heights and Alexandria. June- 

 July. Southeastern U. S. {Gonolobus carolinensis R. Br.; G. hirsutus of Ward's 

 Flora.) 



Pods and seeds indistinguishable from those of V. obliquum. 



2. GONOLOBUS Michx. 



1. Gonolobus laevis Michx. Sand vine. 



Low thickets along the Potomac; common. July-Aug. Southern U. S. {En- 

 slenia albida Nutt.; Ampelanus albidus Britton.) 



3. ACERATES Ell. 



1. Acerates viridiflora (Raf.) Eaton. Green-flowered milkweed. 



Common, though inconspicuous, in the drier open country of our region. July; fr. 

 Oct.-Nov. Eastern U. S. 



4. ASCLEPIAS L. Milkweed. 



Leaves whorled, at least at one of the nodes. 

 Leaves linear; pods 6-8 cm. long, about 5 mm. thick. Corolla greenish white. 



1. A. verticillata. 



