AMBROSIACEAE 1151 



above, petioled, the lower 2-pinnatifid, the upper 1-pinnatifid, the segments often toothed, 

 acute or acuminate : racemes of staminate heads several or numerous, 5-18 cm. long ; in- 

 volucre 3. 5-5 mm. broad, pubescent : pistillate heads mostly solitary : fruit 3-4 mm. long, 

 with an abrupt tip and 4 short tubercles, or these wanting. 



On moist prairies, the Northwest Territory to Illinois.Texas, Mexico and California. 



4. IVA L. 



Annual or perennial herbs, or shrubby plants, with glabrous or coarsely pubescent 

 foliage. Leaves opposite, or alternate above : blades narrow or broad, entire or toothed, 

 often fleshy. Heads solitary or variously disposed. Involucre campanulate, hemispheric 

 or cup-shaped : bracts few, distinct or partially united. Receptacle bearing with linear 

 or spatulate chaff. Flowers inconspicuous, the marginal 1-6, pistillate, fructiferous, with 

 tubular or obsolete corollas : disk-corollas perfect, not fruit-producing : corolla normal : 

 tube funnelform ; lobes 5 ; stigmas simple, dilated above. Anthers entire at the base, with 

 mucronate appendages. Achene broadest above the middle, without pappus. MARSH 

 ELDER. 



Heads subtended by bracts similar to the leaves or conspicuous bracts. 

 Involucres peduncled. 



Leaf-blades entire : involucre with 6-9 bracts. 



Leaf-blades glabrous, 2-5 cm. long : involucres 4-5 mm. high. 1. I. imbricata. 



Leaf-blades strigose, 8-15 mm. long : involucres about 2 mm. high. 2. /. asperifolia. 



Leaf-blades toothed : involucre with 4-5 bracts. 3. I. frutescene. 



Involucres sessile. 



Bracts subtending the heads ovate-lanceolate or rhomboidal. 4. L ciliata. 



Bracts subtending the heads linear or nearly so. 



Leaf-blades ovate or elliptic. 5. I. caudata. 



Leaf-blades linear or nearly so, or linear-filiform. 



Foliage glabrous or nearly so : fructiferous flowers 3. 6. L microcephala. 



Foliage strigose-hirsute or hirsute : fructiferous flower 1. ' 7. /. angustifolia. 



Heads subtended by inconspicuous bracts or naked. 8. L xanthiifolia. 



1. Iva imbricata Walt. Perennial, smooth and glabrous, the foliage honey-scented. 

 Stems erect or decumbent, 3-7 dm. long, branching : leaves fleshy, numerous, mostly 

 alternate ; blades narrowly linear-subulate to linear, 2-5 cm. long, acute, entire or barely 

 repand, sessile : heads drooping, short-peduncled, subtended by linear bracts : involucre 

 campanulate, 4-5 mm. high : bracts suborbicular or oblong-orbicular, obtuse or retuse : 

 corolla 4-5 mm. long, sparingly glandular ; lobes ovate, acute, recurved : achenes 2 mm. long. 



In sand on the coast, Virginia to Florida and Louisiana. Summer and fall. 



2. Iva asperifolia Less. Stem 2-4 dm. tall, simple or sparingly branched : leaves 

 opposite on the lower part of the stem ; blades mainly linear-lanceolate, 8-15 mm. long, 

 acute, entire, strigose, narrow to the base : spikes slender : heads drooping, surpassed by the 

 subtending bracts : involucre somewhat 3-angled, obpyramidal, about 2 mm. high. 



In waste places, near Pensacola, Florida. Native of Mexico. Spring to fall. 



3. Iva frut^scens L. Perennial, shrubby or herbaceous. Stems erect, 1-3.5 m. 

 tall, branching, minutely pubescent or puberulent : leaves mainly opposite, often pubescent 

 like the stem ; blades ovate to linear, 5-10 cm. long, acute, serrate, acuminate to cuneate 

 at the base, short-petioled : bracts narrowly linear, usually surpassing the heads : heads 

 drooping, short-peduncled : involucre campanulate, 3-3.5 mm. high, often broader than 

 high ; bracts orbicular to orbicular-cuneate, obtuse : corolla funnelform or in the fruit- 

 producing flowers tubular, 2-2.5 mm. long ; lobes ovate, acute : achenes broadly cuneate- 

 obovate. 



On beaches and brackish shores, Massachusetts to Florida and Texas. Summer and fall. 



4. Iva ciliata Willd. Annual, strigose-hispid or hispidulous. Stems erect, 5-18 

 dm. tall, simple or branching, commonly mottled : leaves opposite or nearly so ; blades 

 ovate, elliptic or oval, 4-10 cm. long, acuminate, serrate, narrowed into short petioles : 

 spikes 3-20 cm. long, usually continuous : bracts ovate-lanceolate to rhomboidal, acumi- 

 nate, ciliate : heads drooping : bra'cts of the involucre 3-5, obovate to suborbicular, some- 

 times broader than high, about 2 mm. long : staminate flowers 10-15 : fructiferous flowers 

 3-5 : corolla 1.5-2 mm. long : achenes 3 mm. long. 



In moist soil, Nebraska to Louisiana, Texas and New Mexico. Summer. 



5. Iva caudata Small. Annual, hispid or somewhat strigose. Stems erect, 4-10 

 dm. tall, branching, ridged : leaves opposite or nearly so ; blades ovate or elliptic, 4-10 

 cm. long, coarsely and irregularly serrate or incised, acuminate, acute to truncate at the 

 base ; petioles ^-^ as long as the blades, bristly : spikes continuous or interrupted below, 

 conspicuously bracted : bracts linear or with a narrowly elliptic base and linear tip, 7-15 



