Rio Arriba, San Miguel, Bernalillo, Torrance, Taos, Colfax and Valencia cos.) 

 and Ariz. (Apache and Navajo cos.), late summer to fall; Que. to Alta, and s. 

 to D.C., O., Mo., Tex., N.M. and Ariz. 



21. Madia Mol. Tarweed 

 About 17 species, native to western North America and in Chile. 



1. Madia glomerata Hook. Fig. 756. 



Glandular and hairy odoriferous annual, to about 8 dm. tall, usually much 

 smaller; stems simple or with ascending branches; leaves linear to linear-lanceolate, 

 usually 2-7 cm. long and 1-5 mm. wide; heads glomerate in 1 to many very 

 small clusters; involucre fusiform, 6-9 mm. high, about 3-5 mm. wide; rays 

 inconspicuous, yellow, about 2 mm. long, mostly 1 to 3 or wanting from some 

 heads; disk flowers usually several, fertile, their subtending bracts becoming like 

 those of the rays in few-rayed or rayless heads. 



In wet meadows and marshes about lakes and ponds, in N.M. (Rio Arriba Co.) 

 and Ariz. (Coconino Co.), June-Sept.; Sask. and B.C., s. to n. N.M., n. Ariz, and 

 Calif. 



22. Ambrosia L. Ragweed 



Annual or perennial herbs (when perennial usually proliferating from runner- 

 like roots), 2-30 dm. tall, leafy, resinous and aromatic with glandular trichomes; 

 leaves alternate or opposite at the lower nodes (in some species opposite nearly 

 throughout), entire or palmately lobed or (usually) pinnately lobed or dissected, 

 usually petiolate; ray flowers absent; heads unisexual, both staminate and pistillate 

 borne on the same plant; staminate usually in narrow elongate racemelike or 

 spikelike aggregations; pistillate clustered in axils of leaves and bracts below; 

 staminate heads nodding, usually hemispheric; phyllaries few, uniseriate, more 

 or less united; involucre frequently oblique by elongation of the portion away 

 from the stem; receptacle flattish, chaffy throughout (the pales narrow); flowers 

 several to many with rudimentary pistil (pistillodium) and wholly aborted ovaries; 

 anthers usually more or less separated at anthesis; pappus absent; pistillate heads 

 with one or few flowers; phyllaries fused about flowers to form a hard indehiscent 

 nutlike receptacle, the phyllary tips more or less evident as spiny processes that 

 project from the surface of the involucral body at maturity; flowers lacking 

 pappus, corolla and androecium. Franseria Cav. 



A predominantly American genus with approximately 43 species, many of these 

 being desert shrubs. They are wind-pollinated, the pollen of all species being 

 highly allergenic. 



1. Tubercles or spines of the pistillate head scattered in several series over the 

 body of the fruiting involucre 1. A. Grayi. 



1. Tubercles or spines of the pistillate head in a single series (or absent) near 



the apex of the fruiting involucre (2) 



2(1). Plant annual; cauline leaves distinctly petiolate, lobed; staminate head 

 with 3 striations on distal lobes 2. A. trifida. 



2. Plant perennial; cauline leaves subsessile, pinnatifid; staminate head without 



striations on distal lobes 3. A. psilostachya. 



1. Ambrosia Grayi (A.Nels.) Shinners. 



Upright perennial herb, proliferating by adventitious shoots from runnerlike 

 underground roots, forming large colonies; leaves alternate; blades narrowed to 

 petiolar bases to 5 cm. long, with several small lobes below the main expanded 

 blade portion; main bladelike portion obovate-deltoid to lanceolate, to 1 dm. long 

 and 8 cm. broad, irregularly pinnately lobed, major basal lobes and terminal 



1642 



