242 PITTONIA. 
STUDIES IN THE Composit 4.— VIII. 
1. Type of the Bidentidezx. 
By the term Bidentideæ I would designate a certain group 
of plants, to my mind a very natural one, of which the 
genus Bidens is typical. It embraces such other genera as 
Coreopsis, Cosmos, Thelesperma, Heterosperma and Dahlia; 
all these and as many more genera very closely allied, are 
admitted by the conservative Bentham as valid, and made 
to constitute his subtribe Coreopsidese of the Helianthoidee. 
I see no marks of real affinity between any of these plants 
and the true Helianthus allies. By the remarkable charac- 
teristics of their double involucre, as well as in important 
matters of floral structure, they stand entirely aloof, as it 
seems to me, from ali helianthoids. That certain of the 
latter, Actinomeris and Verbesina for example, have flattened 
and two-armed achenes, no more necessarily connects the 
Bidentidez to the Helienthoides than the same conforma- 
tion and crowning of the achenes of Boltonia connects either 
of the aforenamed to the Asteroides. Such empirical taxon- 
omy was in its prime a century and a half ago, when both 
Actinomeris and Verbesina were included in Bidens, as the 
asteraceous Boltonia also might have been, if that type had 
then been known. 
The Bidentidex are a group so exceedingly natural that 
one of Mr. Bentham’s most worthy contemporaries proposed 
to merge the whole group in one genus Bidens; a proposi- 
tion which, as I shall presently show, is fully as logical as 
that of Mr. Bentham, who himself admits severl genera for 
which, according to his criteria, no characters exist. 
