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.arizonica 



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



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 



Ximenesia Cavanilles 1793 



(Named for Ximenes, a Spanish physician) 



(Verbesina L.) 



PI. 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 ARROWHEAD 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 steins and basal simple 

 leaves. 



