CONTRIRUTIONS FROM THE GRAY HERBARIUM OF 

 HARVARD UNIVERSITY, NEW SERIES, No. X. 



By B. L. Robinson and J. M. Greenman. 



Presented May 13, 1896. 



I. — REVISION OF THE GENUS TRIDAX. 



TRIDAX, L. (Name supposed to come from rpt's, thrice, and SaKctv, 

 to bite, referriug to the trifid rays.) — Heads terminal upon long peduncles, 

 heterogamous and radiate or rarely homogamous and discoid. Involucre 

 campanulate to sub-cylindric, 2 - several-seriate, very rarely sub-uni- 

 seriate ; scales all or at least the inner scarious and commonly purple- 

 margined. Receptacle mostly conical. Ray-flowers, when present, 

 fertile ; ligules yellow, white, or roseate, clearly or obsoletely bilabiate ; 

 external lip 3-toothed or deeply trifid, obovate or oblong in outline, 

 patulous; the inner of 1 or 2 short erect teeth or sometimes wanting; 

 disk-flowers usually (if not always?) yellow, regular, o-toothed. Anthers 

 short, sagittate at the base, appeudaged at the apex. Style-branches 

 terminating in short or long subulate appendages. Achenes turbinate, 

 hirsute or upwardly silky-villous, very rarely glabrous or nearly so. 

 Pappus of several to many narrow ciliate scales attenuate to plumose 

 awns (except in G. duhia). — Hort. Cliff. 418, & Gen. no. 979; DC. 

 Prodr. v. 679 ; Benth. & Hook. f. Gen. ii. 392 ; HofFm. in Engl. & 

 Prantl, Nat. Pflanzenf. iv. Ab. 5, 247. BartoUna, Adans. Fam. ii. 124. 

 Sogalgina, Cass. Bull. Philom. 1818, & Diet. Sci. Nat. xlix. 397. Balbisia, 

 •AVilld. Spec. iii. 2214. Galinsogea, HBK. Nov. Gen. & Spec. iv. 252, 

 t. 386. PtUostephium, HBK. 1. c. 253, t. 387, 388. Carphostelphium, 

 Cass. Diet. Sci. Nat. xliv. 62. Mandonia^VfeAdi. Bull. Soc. Bot. Fr. xi. 

 50, t. 1, not Schz. Bip. — Pubescent annuals or perennials not rarely lig- 

 nescent at the base, with leaves opposite, petiolate or subsessile, subentire 

 or more often dentate or irregularly cleft or pinnatifid. About 22 known 

 species, two of them of the S. American Andes, the others confined to 

 Mexico, except a single species which extends also to Mauritius and 

 E. India. 



