188 
Spring Flora of Oklahoma 
Rays few. 
Receptacle naked; achenes fusiform, terete; pappus 
of bristles and scales. V. Chaetopappa. 
Receptacle chaffy; achenes flat; pappus none. 
XXV. Achillea. 
Rays none. 
Receptacle chaffy. 
Pappus none. IX. Filago. 
Pappus of 2 retrorsely, hispid awns or scales. 
XIX. Thelesperma. 
Pappus of 5 or 6 acute or acuminate, ovate or 
lanceolate scales. XX. Marshallia. 
Pappus of 5 to 12 awned scales. XXIV. Gaillardia. 
Receptacle naked. 
Pappus of capillary bristles. 
Plants dioecious or polygamo-dioecious. 
Shrubs; leaves mostly toothed. 
VIII. Baccharis. 
Herbs; leaves entire. X. Anteimaria. 
Plants not dioecious, flowers all fertile. 
XI. Gnaphalium. 
Pappus of thin obtuse scales. 
XXI. Hymenopappus. 
Receptacle bristly. 
Leaves prickly. XXVII. Cirsium. 
Leaves not spiny. XXVIII. Centaurea. 
I. SIDERANTHUS Fraser. 
Annual or perennial herbs with alternate, simple to pin- 
natifid leaves and numerous, rather large heads of yellow 
flowers with yellow rays. Leaves small, toothed or pin- 
natified, sessile. Involucre campanulate, many-flowered, the 
