FAM. L78, 141 



or wanting; calyx a mere border or absent; ovary 1-celled 

 with 2 hairy stigmas; achenes naked, or enclosed in the 

 accrescent nut-like or bur-like involucre. 



1. Sterile and fertile flowers in different heads; — the sterile heads in 

 terminal spikes or racemes, the fertile heads solitary or clus- 

 tered below the sterile; the staminate involucres cup-shaped 

 of 5-12 partially united bracts and 5-20 flowered; receptacle flat, 

 naked or with filiform chaff; the pistillate involucres turbinate or 

 subglobose. 1-flowered, with several spines or tubercles in one 

 row; corolla wanting; achenes without pappus; flowers whitish. 

 Summer and Fall. ------- Ambrosia, Ragweed 



A. hispida. Hirsute to hispid; leaves mostly opposite, 2-3 pinnatifid, 

 or pinnately divided; receptacle chaffy. Dune-sand. 

 1. Sterile and fertile flowers in the same heads; — heads small, axillary, 

 drooping; bracts of the involucre few; receptacle chaffy; flow- 

 ers inconspicuous, whitish; the marginal ones, 1-6, pistillate 

 with tubular corollas; the central ones perfect but sterile, with 

 funnelform corolla, 5-lobed; achenes without pappus. Summer 

 and Fall. -------- iva, Marsh Elder 



I. imbricata. Somewhat shrubby, smooth; leaves mostly alternate, numer- 

 ous, fleshy, linear, entire, sessile; heads short-peduncled; bracts 6-9 sub- 

 orbicular. In sand, on the coast. 



I. frutescens. Shrubby; leaves mostly opposite, pubescent, ovate to linear, 

 serrate, short-petioled; heads short-peduncled; bracts 3-5, orbicular. Salt 

 marshes. 



I. microcephala. Annual, rough; leaves often alternate, narrowly linear, entire 

 or slightly toothed; heads sessile; bracts 3-5, narrowly linear. Dry pine- 

 land. 



173. Carduaceae, Thistle Family. 



Herbs, rarely shrubs with opposite, alternate, or all 

 basal leaves without stipules; flowers in a head, on a re- 

 ceptacle, surrounded by an involucre; calyx of bristles, 

 awns or scales, forming pappus at maturity, or calyx ab- 

 sent; corolla of 5 petals, for the greater part united; sta- 

 mens 5, alternate with the corolla-lobes, the anthers syn- 

 genesious; ovary inferior, 2-carpeled, 1-celled, with 1 style 

 and 2 stigmas; fruit an achene. 



1. Heads discoid, i. e. corollas all tubular, ------- 2 



1. Heads radiate, i. e. central corollas (disk-flowers) tubular, and mar- 



ginal corollas (ray-flowers) ligulate, - - - - - - -12 



2. Heads with the flowers all perfect. --------3 



2. Heads with the central flowers perfect, marginal flowers pistillate. - - 1 1 



Heads dioecious; — shrubs with alternate leathery leaves and heads 

 in corymbs or panicles; bracts in several rows; receptacle flat. 

 pitted, without chaff; corollas of staminate heads tubular, of 

 pistillate heads filiform; pappus of the former short, of the lat- 



