53S 



( It IK ik'IACKAK. 



Vol.111. 



io. Nabalus crepidineus ( Michx.) DC. Corymbed Rattlesnake-root. Fig. 41 19. 



1'rcnanthcs crcfidinea Michx. Fl. Bor. Am. 2: 84. 1803. 

 Nabalus crepidineus DC. Prodr. 7: 242. 1838. 



Stem glabrous or very nearly so below, corym- 

 bosely branched and sometimes puberulent above, 

 stout, 5-a high. Leaves thin, the basal and lower 

 ones hastate, ovate, oblong, or deltoid, sharply den- 

 tate, lobed, or incised, sometimes 10' long, usually 

 with broadly winged petioles; the upper much 

 smaller, sessile or short-petioled, narrowed at the 

 base, not clasping, ovate, deltoid, or lanceolate, 

 acute ; heads numerous, pendulous, short-peduncled, 

 corymbose-paniculate, 4"-6" broad, 20-35-flowered ; 

 involucre oblong or oblong-campanulate, hirsute, 

 S"-8" long, about 3" thick, dark green or purplish, 

 its principal bracts 12-15, with several very short 

 outer ones; flowers cream color; pappus brown. 



In fields and thickets, western Pennsylvania and New 

 York to Kentucky, west to Minnesota and Kansas. 

 Aug.-Oct. 



Family 45. AMBROSIACEAE Reichenb. Consp. 112. 

 Ragweed Family. 



1828. 



Annual or perennial herbs, monoecious, or sometimes dioecious, many of them 

 weeds, some shrubby, with alternate leaves, or the lower opposite, and small heads 

 of greenish or white flowers subtended by an involucre of few, separate or united 

 bracts, the pistillate heads sometimes larger and nut-like or bur-like. Staminate 

 and pistillate flowers in the same heads, or in separate heads. Receptacle chaffy. 

 Pistillate flowers with no corolla, or this reduced to a short tube or ring; calyx 

 adnate to the i-celled ovary, its limb none, or a mere border; style 2-cleft. Stami- 

 nate flowers with a funnelform tubular or obconic 4-5-lobed corolla; stamens 

 mostly 5, separate, or their anthers merely connivent, not truly syngenesious, with 

 short inflexed appendages ; ovary rudimentary ; summit of the style often hairy 

 or penicillate. 



Eight genera and about 60 species, mostly natives of America, a few only of the Old World. 



Staminate and pistillate flowers in the same heads ; involucre of a few rounded bracts, i. Iva. 

 Staminate and pistillate flowers in separate heads, the staminate mostly uppermost ; involucre of 

 the pistillate heads bur-like or nut-like. 

 Involucral bracts of the staminate heads united. 



Involucre of the pistillate heads with several tubercles or prickles in a single series. 



2. Ambrosia. 

 Involucre of the pistillate heads with numerous prickles in several series. 3. Gaertneria. 



Involucral bracts of the staminate heads separate ; involucre of pistillate heads an oblong bur. 



4. Xanthiiint. 



i. IVA L. Sp. PI. 988. 1753. 



Puberulent or scabrous herbs, with thick opposite leaves, or the upper alternate, and 

 small nodding, axillary and solitary, spicate racemose or paniculate heads of greenish flowers. 

 Involucre hemispheric or cup-shaped, its bracts few, rounded. Receptacle chaffy, the linear 

 or spatulate chaff enveloping the flowers. Marginal flowers 1-6, pistillate, fertile, their corollas 

 short, tubular or none. Disk-flowers perfect, sterile, their corollas funnelform, 5-lobed. their 

 styles undivided, dilated at the apex. Anthers entire at the base, yellow, scarcely coherent 

 with each other, tipped with mucronate appendages. Achenes compressed, obovoid, glabrous. 

 Pappus none. [Named after Ajuga Iva, from its similar smell.] 



About 15 species, natives of America. Besides the following, 7 others occur in the southern 

 and western United States. Type species: Iva annua L. 



Heads spicate or racemose, each subtended by a linear or oblong leaf. 

 Heads solitary, pedicelled. 



Bracts of the involucre 4-5 ; heads i}4"-2" high. 



Leaves serrate, oval or oblong; eastern. 1. I. frulescens. 



Leaves entire or nearly so. obovate or oblong; western. 2. /. axillaris. 



Bracts of the involucre 6-9 ; heads 3" 4" high ; southeastern. 3. 7. imbricata. 



Heads spicate-paniculate ; leaves dentate. 4. /. ciliata. 



Heads spicate-paniculate, not subtended by leaves. 5. /. xanthiifolia. 



