DESCRIPTIONS OF SOME COMMON WEEDS 209 



cyme ; corolla lobes nearly erect, tube not longer than the 

 lanceolate segments of the calyx, greenish white ; appears 

 in July and August. Common species eastward and 

 troublesome as a weed in northern Mississippi Valley. 



Milkweed Family (Asclepiadaceae.) Perennial herbs, 

 vines, or shrubs, with milky juice and entire, opposite, or 

 whorled leaves; flowers in umbels, regular; calyx infe- 

 rior, corolla bell or urn shaped, rotate or funnel form, 

 five-lobed or five-cleft, segments generally reflexed; 

 crown between the corolla and stamens ; stamens five, in- 

 serted on the corolla, generally monadelphous, anthers 

 connivent around the stigma, or more or less united with 

 each other, commonly bearing an erect or inflexed mem- 

 brane; pollen collected in masses, generally ten, known 

 as pollinia ; ovary of two carpels, in fruit of two follicles, 

 seeds flattened, usually appendaged by a long tuft of 

 hairs called a coma. About 200 genera containing 1,800 

 species widely distributed, many members of the order 

 being weedy, some medicinal and a few economic. 



Showy Milkweed (A. speciosa, Torr.). A perennial 

 from one to four feet high, white tomentose or canescent ; 

 leaves thick, broadly ovate or oval, petioled ; pedicel 

 glabrate above, flowers borne in dense umbels or merely 

 solitary, the pedicels stout ; corolla purplish green, large ; 

 follicle erect or spreading on the recurved pedicels. In 

 Iowa, Minnesota, Nebraska, Kansas, Utah, California and 

 British Columbia. Very common at times in grain fields 

 and meadows. The swamp milkweed (A. incarnata) has 

 acuminate leaves ; flowers in umbels, which are numerous 

 and many-flowered ; corolla red or rose-purple or rarely 

 white, the incurved horns longer than the hood, follicles 

 erect. Common in swamps in the North. The butterfly 

 weed (A. tuberosa) has alternate, ligulate or oblong ses- 

 sile leaves; flowers in cymose umbels, bright orange or 

 yellow. Common on prairies, sandy fields and openings. 

 The white milkweed (A. verticillata) has fascicled roots, 



