252 BOTANICAL INFORMATION. 
Note on the genus Thelesperma of Lessing, óy Asa Gray, M. D. 
Tn examining the Composite of the Herbarium formed by the U.S. 
Exploring Expedition under Captain Wilkes, I noticed among those 
gathered at Rio Negro, Northern Patagonia, a plant which struck me 
as being a close congener of the Cosmidium gracile, Torr. and Gray, Fl. 
North Am. vol.ii. p. 350; and I was pleased to find this genus re- 
presented in the region of extra-tropical South America, which so nearly 
corresponds to that district of North America to which belong the 
three species of Cosmidium already described. It was at once apparent, 
however, that this southern plant is no other than the Bidens Mega- 
potamica, Spreng., and the Thelesperma scabiosoides of Lessing. The 
genus Thelesperma is so well characterized in De Candolle's Prodromus, 
that I see not how the resemblance should have been unobserved when 
the genus Cosmidium was founded; except that the latter was chiefly 
established on the radiate C. filifolia, with neutral rays, while Thele- 
sperma, though founded on a rayless species, is placed among the 
Verbesinee, where the rays are pistillate. With the specimens before 
me there can be no question that our genus Cosmidium must be merged 
in the much earlier genus of Lessing; at most, it can only be retained 
as a sectional name for the radiate species; as follows :— 
THELESPERMA, Less. in Linnea, and Syn. p. 234. DC. Prod. vol. v. 
p. 633. (Cosmidium, Torr. and Gray, Fl. N. Am., vol. ii. p. 350.) 
$ 1. TugLESPERMA vera, Less. — Capitulum homogamum discoideum. 
T. scabiosoides, Less. l.c. Hook. et Arn. Journ. Bot. vol. iii. p. 319. 
Bidens Megapotamica, Spreng. Syst. vol. iii. p. 424. Southern 
Brazil and North Patagonia. 
T. gracile, — Bidens gracilis, Torr. in Ann. Lyc. New York, vol. ii. 
p.215. Cosmidium gracile, Torr. and Gray, l.c. Gray, Pl. Fendl. 
p.86. Upper Arkansas to New Mexico. 
§ 2. Cosmiprum.—Capitulum sepius 8-radiatum, ligulis neutris. 
T. simplicifolia,—Cosmidium simplicifolium, Gray, Pl. Fendl. p. 86. 
orthern Mexico. 
T. filifolium,—Coreopsis filifolia, Hook. Bot. Mag. t. 8505. DC. Prod. 
vol. v. p. 290. Cosmidium filifolium, Torr. and Gray, l.e. Plains 
of Arkansas and Texas. 
