214 CONTRIBUTIONS TROM THE NATIONAL HERBARIUM. 



8. OENOTHERA L. Evening primrose. 



1. Oenothera biennis L. 



Open places; common. July-Sept. Eastern N. Amer. 



An extremely variable species, in recent years the subject of extensive investiga- 

 tions in plant breeding. The species ia considered to consist of numerous "elementary 

 species, " three of which have been described by Bartlett' from our region: 0. steno- 

 meres, 0. brevicapsula, and 0. ruderalis. 0. stenomeres is a form with linear petals. 



9. RAIMANNIA Rose. 



1. Baimannia laciniata (Hill) Rose. 



Dry open places, northeastward; infrequent. May-July, Eastern U, S. (Oeno- 

 thera sinuata L.; 0. laciniata Hill.) 



10. KNEIFFIA Spach. Sundrops. 



Flowers small (usually 1 cm. broad or less). Flowers mostly borne on the upper third 



of the plant and separated from the main leafy portion by an elongate internode. 



1. K. pumila. 

 Flowers large (1.5-2.5 cm. broad or more). 



Pedicels elongate, longer than the capsule 2. K. longipedicellata. 



Pedicels shorter than the capsule. 



Capsule markedly club-shaped, tapering from the summit to the base. 



3. K. linearis. 



Capsule oblong or nearly so, tapering slightly at the base 4, K. fruticosa. 



1. Kneiffia pumila (L.) Spach. 



Woods and open places; infrequent. May-June. Eastern N. Amer. (Oenothera 

 pumila L.) 



2. Kneiffia longipedicellata Small. 



Moist soil, chiefly eastward; frequent. May-July. Eastern U. S. (Oenothera 

 longipedicellata Robinson.) 



3. Kneiffia linearis (Michx.) Spach. 



Dry fields; frequent. May- June. Eastern U. S. (Oenothera fruticosa linearis S. 

 Wata.; 0. linearis Michx.) 



4. Kneiffia fruticosa (L.) Raim. 



Dry soil; common. May-June. Eastern U. S. (Oenothera fruticosa li.) 



Trapa natans L., of the family Trapaceae, native of Eur., was formerly established 

 in fish ponds in Potomac Park but is now extinct. 



113. HALORAGIDACEAE. Water milfoil Family. 



Leaves all dissected into hairlike lobes 1. MYBIOPHYLLUM. 



Leaves, at least the upper ones, simple, shallowly toothed, the lower ones usually 

 dissected 2. PBOSEEPINACA. 



1. MYRIOPHYLLT7M L. Water milfoil. 



1. Myriophyllum spicatum L. 



Hunting Creek. Widely distributed in N. Amer., Eur., and Asia. 



Myriophyllum proserpinacoides Gill., parrot's-feather, a native of Chile, is cultivated 

 in aquaria. For several years this plant has been grown in two fountains on the north 

 side of the Treasury Building, where it makes a striking display and attracts much 

 attention. 



' Cybele Columb. 1: 37-56. 1914. 



