134 COMPOSITES. (composite family.) 



more scarious interior ones, these subtending the fertile flowers. Receptacle convex, 

 with linear-oblong or spatulate chaffy bracts subtending the outer series of sterile 

 flowers, but mostly minute or wanting to the inner flowers. Akenes oblong-obovate, 

 glabrous, wingless, but acute-margined, with an incurved apiculatiou inserted by a 

 very small base, falling away at maturity with the involucral and two receptacular 

 bracts, but these readily separating. Pappus none, and corolla deciduous. 

 # * Fertile flowers apetalous, or with corolla reduced to a tube or ring around the base of 

 the 2-parted style ; disk-flowers staminate, anthers slightly united and their short ter- 

 minal appendage inflexed, the abortive style hairy only at the somewhat enlarged and 

 depressed summit, the ovary a mere rudiment : pappus none (or a vestige in Nos. 26 

 and 27) : heads small ; the flowers whitish or greenish, 

 -i- Head androgynous (rarely all male in No. 27), having few female flowers at the margin ; 

 the more numerous male flowers all or most of them subtended by slender and com- 

 monly spatulate chaffy bracts: involucre open. 



**■ Akenes turgid, mostly obovate or pyriform, marginless. 



25. Iva. Female flowers 1 to 5, with or without the tube or cup representing a corolla. 



Akenes more or less obcompressed, glabrous, puberulent, or glandular : the terminal 

 areola small. 



26. Oxytenia. Female flowers about 5, wholly destitute of corolla. Involucre of about 



5 dilated-ovate and rather rigidly acuminate bracts. Receptacle convex, small : the 

 10 to 20 sterile flowers subtended by slender chaffy bracts with cuneate-dilated tips. 

 Akenes (immature) very villous, nearly pyriform, with large terminal areola bearing 

 around the base of the style a fleshy annular disk. Lower part of the disk-flowers 

 and their chaff beset with some villous hairs. 



++ ++ Akenes flattened, obcompressed, wing-margined. 



27. Dicoria. Female flowers one or two, wholly destitute of corolla : male flowers 6 to 



12, with mere rudiments of ovary and style. Involucre of 5 oval or oblong herbaceous 

 bracts ; and within one or two larger and broad thin-scarious bracts, subtending the 

 fertile flowers, or these wanting in male heads. Receptacle small, flat, with a few 

 narrow and hyaline chaffy bracts. Filaments monadelphous up to the lightly con- 

 nected anthers. Akenes much surpassing the outer involucre, oblong, anteriorly flat, 

 convex or somewhat angled dorsally, abruptly bordered by a thin-scarious pectinate- 

 dentate wing or edge. Pappus rudimentary, of several small and setiform bracts. 



■»- ■»- Heads unisexual, moncecious ; the fertile with solitary or 2 to 4 completely or nearly 

 apetalous female flowers in a closed nutlet-like or bur-like involucre, only the style- 

 branches ever exserted ; the sterile of numerous male flowers in an oxien involurre, 

 the heads in a raceme or spike : akenes turgid-obovoid or ovoid, wholly destitute of 

 pappus : flowers greenish or yellowish. 



4+ Involucre of the sterile heads gamophyllous : the receptacle low, and abortive style with 

 dilated apex radiately fimbriate. 



28. Ambrosia. Involucre of the male flowers from depressed-hemispherical to turbinate, 



ft to 12-lobed or truncate, herbaceous. Receptacle flat or Cattish, usually with some 

 filiform chaff among the outer flowers. Involucre to the solitary fertile flower nut- 

 like, apiculate or beaked at the apex, and usually armed with 4 to S tubercles or 

 short spines in a single series below the beak. Sterile heads spicate or racemose 

 above the fewer fertile ones. 



29. Franseria. Heads of male flowers as Ambrosia, or sometimes intermixed with the 



female. Fertile involucre 1 to 4-flowered, 1 to 4-celled, a single pistil to each cell, 1 t» 

 4-rostrate, more or less bur-like, being armed over the surface with several or numer- 

 ous prickles or spines (the spiny free tips of component bracts) in more than one 

 series. Leaves mostly alternate. 

 ++ ++ Involucre of the sterile heads polyphyllous : the receptacle cylindraceous. 



30. Xanthium. Involucre of the globular sterile heads one or two series of small narrow 



bracts : receptacle distinctly chaffy, a cuneate or linear-spatulate chaffy bract partly 



, enclosing each male flower : filaments monadelphous. Fertile heads a closed and 



ovoid bur-like 2-celled and 2-flowered involucre, 1 to 2-beaked at the apex, the surface 



