186 AMBROSIACEAE 



8. HIERACIUM L. 



Perennial herbs with corymbose-paniculate yellow flowers. Involucre 

 cylindric and scarcel}' imbricated (in ours). Achenes ribbed, beakless, 

 and fusiform (in ours). Pappus of brownish bristles. 



1. H. longipilum Torr. Prairik Hawkweed. 1°-3° high, naked 

 above : leaves oblong-spatulate, entire : stems and leaves densely very 

 long-pnbescent : involucre and peduncles glandular-bristly. — Prairies 

 around Lee's Summit. Rare and local. July-September. 



9. NABALUS Cass 



Leafy-stemmed perennial herbs with (in ours) greenish-white, racemose- 

 paniculate flowers. Involucre cylindric, the bracts in a single row, with 

 smaller bractlets at bas-e Achenes linear-oblong, striate, not contracted 

 above. Pappus of copious bristles. 



1. N. asper ( Michx. ) Torr. & Gray. White Lettuce. 2°-fi° high, 

 rough-pubescent : leaves oblong-lanceolate, sessile, toothed : heads erect, 

 12-25-flowered, in a strict inflorescence : involucre hirsute-pubescent. — 

 Not uncommon in dry woods and prairies throughout the southwestern 

 part. August-September. 



Family 121. AMBROSIACEAE Reichenb. 

 Herbs with greenish flowers in involucrate heads, the staminate and 

 pistillate flowers in the same or in diilerent heads. Receptacle chaffy. 

 Pistillate flowers with no corolla or a very small one and a small calyx, 

 its limb entire or slightly toothed, adnate to the summit of the 1-celled, 

 lovuled ovary. Staminate flowers with a 4-5-lobed corolla. Stamens 

 five, the anthers nearly separate. 



Both kinds of flowers in the same head. 1. IVA. 

 Flowers in different heads. 



Involucre of pistillate flowers not prickly. 2. Ambrosia. 



Involucre of pistillate flowers very prickly. 3. Xanthium. 



1. IVA L. Marsh Elder. 

 Herbs with mostly opposite leaves and greenish-white flowers in small 

 nodding heads. Involucral bracts few, roundish. Marginal flowers per- 

 fect, fertile. Disk flowers perfect, sterile. 



Heads in axils of bracts. 1. I. vilinla. 



Heads not bracted at base. 2. /. xanthiifolia. 



1. I. ciliata Wiild. Annual, rough-pubescent. \°-\° high: leaves 

 ovate, petioletl, dentate : bracts ciliate. Strongly resembles Ambrosia 

 trifida. — Low prairies. Very abundant locally near Atherton, Lake City, 

 Buckner and Levasy. Adventized at Kansas City. August-October. 



2. I. xanthiifolia (Fresen.) Xutt. Annual, 2°-r)° high, softpubes- 

 cent : leaves ovate-dentate, long-petioled, pale beneath, cane.scent : inflor- 

 escence paniculate-spicate. — .\(lventized in waste places at Kansas City 

 and Courtney. August-October. 



