ARROWHEAD FAMILY 299 



WYETHIA Nuttall 1834 

 (Named for Wyeth, a botanical collector) 



Heads with yellowish or white pistillate rays, the latter sometimes with 

 sterile filaments, disk-flowers yellow, perfect, achenes oblong, 4-5-angled, 

 pappus a fringed or 5-10-toothed crown, 1 or more of the teeth often awn- 

 like; receptacle convex, with chaff, involucre bell-shaped, the bracts in 2-3 

 rows; heads solitary; leaves alternate, usually entire; perennial. 



1. Rays white to straw-color W. helianthoides 



2. Rays bright yellow 



a. Rays 2.5-4 cm. long 



( 1 ) Plants smooth throughout W. amplexicaulis 



(2) Plants hairy W. cvrizonica 



b. Rays 10-15 mm. long; plants rough W.scabra 



XANTHIUM Linne 1753 COCKLEBUR 

 (Gr. xanthos, yellow, from yielding a yellow dye) 



Heads without rays, monoecious, staminate heads densely clustered 

 at the ends of branches, the involucre of 1-3 rows of bracts, receptacle 

 cylindric, chaffy, corolla present ; pistillate heads axillary, forming a closed 

 involucre, 1-2-beaked and covered with hooked spines, with 2 achenes, pap- 

 pus none; leaves alternate, lobed or toothed; annual. 

 Stems 1-6 ft. high; leaves ovate to rounded; bur 2-2.5 



cm. long, with hooked or curved beak X. canadense 



Xi MEN ESI A Cavanilles 1793 

 (Named for Ximenes, a Spanish physician) 



PL 40, fig. 5. 



Heads with yellow pistillate ray-flowers, disk-flowers yellow, perfect, 

 achenes flat, winged, pappus of 2 awns or in the ray of 1-3 awns ; receptacle 

 convex, with chaff, involucre hemispheric, the bracts more or less imbricated, 

 equal and spreading; heads solitary or few; leaves alternate or sometimes 

 opposite, simple, toothed ; annual. 

 Stems 1-3 ft. high ; leaves ovate and heart-shaped to 

 lance-ovate, 2-5 in. long; rays 12-15, about an inch 

 long X. encelioides 



ALISMALES ARROWHEAD ORDER 

 ALISMACEAE ARROWIHEAD FAMILY 



Sepals 3, green, petals 3, colored, stamens 6-many, pistils many or rarely 

 few, fruit an achene ; flowers perfect, monoecious or dioecious, in racemes 

 or panicles; aquatic or marsh herbs with leafless stems and basal simple 

 leaves. 



