3i6 
The Ohio Naturalist. 
[Vol. V, No. 6, 
NOTES FROM THE OHIO STATE HERBARIUM. III. 
H. A. Gle,\son’. 
The gexus Bidens ix 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 rays, the second the rayless species with divided leaves, the 
third the Coreopsis-like species with conspicuous rays, and the 
fourth the single species Bidens hipinnata, 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;2S0, 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 by 
K. M. Wiegand (Bull. Torr. Club 26:399-422. 1899.), who gives 
kevs and full descriptions of most of the species of Platycarpae, 
and bv E. L. Greene (Pittonia 4:242-284. 1901.), Avho discusses 
the nomenclatorial history of the genus and describes many new 
species. 
Key to the Ohio Species. 
1. Achenes linear, not flattened. (Psiloc.arp.ae DC.) 1. B. bipinjuita. 
1. Achenes cuneate to obovate, flattened. (Pe.atycarp.ae 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, 0-10 cm. long, little or not at all narrowed at the base. 
2. B. cernita. 
4. Leaves elliptical, 10- IS cm. long, narrowed at the base. 3. B. elliptica. 
5. Outer bracts scarcely exceeding the disk, not more than 15 mm. long. 
4. B. connata. 
