FLORA OF THE DISTRICT OF COLUMBIA. 285 



22. POLYMNIA L. 



Rays 5, obovate or wedge-shaped, shorter than the bracts or but slightly exceeding 

 them, yellowish white; lower leaves pinnately lobed; achenes 3-ribbed, not 

 striate 1. P. canadensis. 



Rays 10-15, narrowly oblong, much longer than the bracts, yellow; lower leaves 

 palmately lobed; achenes conspicuously striate 2. P. uvedalia. 



1. Polymnia canadensis L. Small-flowered leafcup. 

 Damp woods along the Potomac above Washington; common. July-Oct. Eastern 



U.S. 



2. Polymnia uvedalia L. Large-flowered leafcup. 

 Damp woods along the Potomac; common. Aug. -Oct. Eastern U. S. 



23. ACANTHOSPERMUM Schrank. 



1. Acanthospermum australe (Loefl.) Kuntze. Spiny-bur. 



On the Virginia side of the Potomac half a mile beyond the railroad bridge, on the 

 railroad embankment; plants forming a patch 4.5 by 6 meters which has persisted 

 several years. Va. to La.; widely distributed in tropical regions. 



24. SILPHIUM L. 



Silphium laciniatum L., a native of the western and southern states, with pinnati- 

 fid leaves, was reported by Holm as having been foimd at Woodley Bridge; the 

 plant has now disappeared. 



1. Silphium trifoliatum L. Rosin-weed. 



Woods or open fields; frequent. July- Aug. Eastern N. Amer. 



A tall perennial with glabrous stems, finely toothed leaves, and large heads of yel- 

 low flowers. In general appearance it resembles some of our species of Helianthus, 

 but it is easily distinguished by the broad bracts. 



25. CHRYSOGONUM L. 



1. Chrysogonum virginianum L. Golden star. 



Woods; common. Apr .-June; sometimes flowering in early or late autumn. 

 Southern Pa. to Fla. 



The variety dentatum described by Gray ^ scarcely deserves nomenclatorial recogni- 

 tion. It is supposed to have deltoid-ovate, acute, dentate-serrate, rather than ovate, 

 obtuse, crenate leaves, but in these respects there is no constant difference. It was 

 described from material collected on High Island. 



26. PARTHENIUM L. 



* 



1. Parthenium integrifolium L. 



Collected but once, on a dry hillside neartheHyattsville Swamp, in 1909 (Standley). 

 Eastern U. S. 

 'A coarse rough-hairy perennial with small heads of whitish flowers. 



27. HELIOPSIS Pers. 



1. Heliopsis helianthoides (L.) Sweet. Ox-eye. 



Woods; chiefly along the Potomac. July-Sept. Eastern U. S. {H. laevis Pers.) 

 A coarse perennial with large heads of yellow flowers. 



' Bot. Gaz. 7: 31. 1882. 



