186 
Spring Flora of Oklahoma 
opposite, alternate or basal, ex-stipulate leaves. Flowers 
perfect, pistillate, or neutral, or sometimes monoecious or 
dioecious, borne on a common receptacle, forming heads, 
subtended by an involucre of few to many bracts, ar¬ 
ranged in one or more series. Receptacle naked, or with 
chaffy scales subtending the flowers. Calyx-tube com¬ 
pletely adnate to the ovary, the limb (pappus) of bristles, 
awns, teeth, scales. Corolla tubular, usually 5-lobed or 
5-cleft, or that of the marginal flowers expanded into a 
ligule (ray). Stamens usually 5, borne on the corolla 
and alternate with its lobes, their anthers united into a 
tube (syngenesious). Ovary 1-celled. Fruit an achene. 
Artificial Key to Genera. 
Rays yellow or red. 
Receptacle chaffy. 
Receptacle flat or slightly convex. 
Pappus none, or of two caducous awns. 
XII. Berlandiera. 
Pappus a persistent irregular cleft crown. 
XIII. Engelmannia. 
Pappus of two short teeth or awns or mere border. 
Bracts of the involucre all separate. 
XVIII. Coreopsis. 
Bracts of the involucre united to about the mid¬ 
dle. XIX. Thelesperma. 
Receptacle convex or conic. 
Achenes 4-angled. XIV. Rudbeckia. 
Achenes terete; leaves cordate-clasping. 
XV. Dracopis. 
Achenes compressed, winged. XVI. Ratibida. 
Achenes turbinate. XXIV. Gaillardia. 
