Nur’ 
Family 1. AMBROSIACEAE 
By Per AXEL RYDBERG 
Annual or perennial herbs, or shrubs, usually with bitter or aromatic, often 
more or less glandular-puberulent or glandular-punctate and rough-pubescent 
foliage. Leaves alternate or both alternate and opposite. Flowers through 
abortion monoecious, inconspicuous in small heads; these either unisexual or 
androgynous. Staminate or androgynous heads nodding with few distinct or 
more or less united bracts. Receptacle chaffy; paleae either dilated, usually 
scarious, sometimes accrescent and becoming larger than the bracts, or else 
filiform, or filiform with dilated or clavate tips. Staminate flowers several 
(3-50) in each head; corolla funnelform, with a short narrow tube, hyaline, 
often angled, with 5 ovate or triangular, acute lobes; stamens monadelphous; 
filaments united into a hyaline tube; anthers oblong, distinct or slightly 
coherent at first, with acute or acuminate incurved apices; pistil abortive; 
style usually shorter than the stamens; stigma usually peltate or capitate, 
hispidulous, penicillate, or fimbriate, rarely obsolete and without hairs. Pist- 
illate flowers either few, marginal in the same head as the staminate ones, or 
else in separate heads, and then enclosed in a bur-like involucre formed of one 
or several series of united bracts, those of the different series coalescent, usually 
spiny or with scale-like appendages and prolonged into 1—7 beaks, from which 
the styles protrude; corolla absent or represented by a fleshy ring or short 
truncate tube; pappus none or a mere vestige; styles and stigmas elongate. 
Heads androgynous, not bur- or nut-like, bearing 1-10 pistillate margi- 
nal flowers and more numerous staminate ones in the center (or in 
some heads all the flowers rarely staminate). Tribe 1. IVEAE. 
Heads unisexual, the pistillate ones bur- or nut-like, the involucre wholly 
enclosing the 1-7 pistillate flowers or achenes. Tribe 2. AMBROSIEAE. 
Tribe 1. IVEAE. Herbs or shrubs with small androgynous nodding heads, 
in racemes, spikes, or panicles; staminate flowers numerous, in the center, 
usually subtended by spatulate or filiform-clavate paleae; anthers with short, 
rarely pointed tips, pistillate flowers few, 1-10, marginal, with no corollas or 
rudimentary ones; achenes free. 
Achenes neither strongly flattened nor surrounded by a wing or margin. 
Pistillate flowers not enclosed by broad hyaline paleae. 
Corolla of the pistillate flowers evident, consisting of a truncate tube; 
fruit not woolly. 
Heads spicately or racemosely disposed in the axils of leaf-like 
bracts. Vo wae 
Heads paniculate, not bracted. 2. LEUCIVA. 
Corolla of the pistillate flowers none, represented by a fleshy ring; achenes 
woolly. 3. OXYTENIA. 
Pistillate flowers subtended and usually partly embraced by broad hya- 
line, concave paleae. 
Corolla of the pistillate flowers present; heads solitary, scattered along 
leafy branches, mostly supra-axillary; achenes tubercled on the 
inner face. 4. CHORISIVA. 
Corolla of the pistillate flowers rudimentary; heads paniculate; achenes 
equally muricate on both faces. 5. CYCLACHAENA. 
Achenes strongly flattened, either margined or winged; pistillate flowers sub- 
tended by broad paleae. 
VOLUME 33, ParT 1, 1922] 
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