3i6 The Ohio Naturalist. [Vol. V, No. 6, 



NOTES FROM THE OHIO STATE HERBARIUM. III. 



H. A. Gleasox. 



The genus Bidexs in Ohio. The species of the genus as 

 represented in Ohio fall naturally into four well distinguished 

 groups, the first including the simple leaved forms with or with- 

 out ravs, the second the rayless species with divided leaves, the 

 third the Coreopsis-like species with conspicuous rays, and the 

 fourth the single species Bidens bipinnata, distinguished by its 

 linear achenes and dissected leaves. The latter is our only rep- 

 resentative of the section Psilocarpae of DeCandolle; the others 

 with flat achenes belong to the section Platycarpae. 



The species of the northeastern United States have been 

 confused in the recent floras, and this has led to a misunder- 

 standing of the local forms. The keys and descriptions in this 

 paper include only the Ohio species, and it is hoped that they 

 will be of service to Ohio botanists in studying this interesting 

 genus of Composites. 



A number of species now included in Bidens are in Gray's 

 Manual and other earlier works referred to Coreopsis. Dr. 

 Britton (Bull. Torr. Club 20:280, 281. 1893.) first pointed out 

 their closer relationship with Bidens, including in that genus all 

 forms with a pappus of upwardly or downwardly barbed awns, 

 and limiting Coreopsis to those species in which the pappus con- 

 sists of two short teeth, a mere border, or is entirely absent. 

 The aquatic species known as Bidens beckii differs in many sig- 

 nificant features from typical Bidens, and has been proposed by 

 Professor E. L. Greene as the type of the new genus Megalodonta. 

 The name of the Ohio species becomes accordingly Megalodonta 

 beckii (Torr.) Greene. 



The most important recent literature on the genus is bv 

 K. M. Wiegand (Bull. Torr. Club 26:399-422. 1899.), who gives 

 keys and full descriptions of most of the species of Platycarpae, 

 and bv E. L. Greene (Pittonia 4:242-284. 1901.), who discusses 

 the nomenclatorial history of the genus and describes many new 

 species. 



Key to the Ohio Species. 



1. Achenes linear, not liattened. (Psilocarpae DC.) 1. B. bipi}i}iata. 



1. Achenes cuneate to obovate, flattened. (Platycarpae DC.) 2. 



2. Leaves simple, serrate or somewhat pinnatifid. 3. 



2. Leaves pinnately parted or compound. 6. 



3. Heads nodding on erect peduncles after flowering. 4. 



3. Heads persistently erect. 5. 



4. Leaves oblong, (i-lO cm. long, little or not at all narrowed at the base. 



2. B. ccrnua. 



4. Leaves elliptical. 10- IS cm. long, narrowed at the base. 3. B. cUiptica. 



5. Outer bracts scarcely exceeding the disk, not more than L5 mm. long. 



4. B. connata. 



