1 "Pistillate and staminate flowers in different heads" 2 1 "Pistillate or sterile flowers in same head as staminate or bisexual flowers" 8 2 "Pistillate and staminate heads on same plant [monoecious]" 3 2 "Pistillate and staminate heads on different plants [dioecious]" 6 3 "Subshrub or shrub (to small tree)" Ambrosia 3 Herb 4 4 "Stem armed with 3-branched spines" "Xanthium spinosum" 4 "Stem unarmed" 5 5 "Staminate heads well-spaced in long terminal inflorescence; bur 2--10 mm" Ambrosia 5 "Staminate heads congested; bur 10--30+ mm" "Xanthium strumarium" 6 "Shrub or erect herb with sticky leaves, not woolly" Baccharis 6 "Herb, sometimes prostrate, not sticky; plant generally +- woolly" 7 7 "Stem from rhizome; leaf rosette withered at flower; cauline leaves long, all except distal-most +- equal" "Anaphalis {Anaphalis margaritacea}" 7 "Stem from persistent leaf rosette or thick, often branched caudex; cauline leaves generally +- reduced, at least distal-most short, 1--3 cm" Antennaria 8 "Outer flowers without corollas; heads not embedded in woolly hairs" 9 8 "Outer flowers with (sometimes narrowly cylindric) corollas; heads sometimes embedded in woolly hairs" 12 9 "Heads solitary; plant low, stems often spreading or prostrate" 10 9 "Heads in raceme- or panicle-like clusters" 11 10 "Head on slender +- leafless peduncle; outer fruits stalked, not spine-tipped" Cotula 10 "Head sessile near stem base or at branch tips, +- enveloped by sheathing bases of opposite or whorled subtending leaves, overtopped by branches; fruit sessile, spine-tipped" "Soliva {Soliva sessilis}" 11 "Annual; fruit smooth or warty, generally winged, glabrous or hairy" "Dicoria {Dicoria canescens}" 11 "Subshrub or shrub; fruit long-soft-hairy, not winged" "Euphrosyne acerosa" 12 "Outer flowers sterile; head not very small, not embedded in woolly hairs" 13 12 "Outer flowers pistillate [corolla often narrowly cylindric]; heads sometimes very small, embedded in woolly hairs" 18 13 "Cauline leaves generally bladeless, sheathing; basal leaves from creeping rhizome, often appearing after flower stem, long-petioled, palmately lobed" "Petasites {Petasites frigidus var. palmatus}" 13 "Cauline leaves with blades, sometimes reduced distally on stem, not sheathing; basal leaves 0 or from taproot, appearing before flower stem, sessile or petioled, entire to 1--2-pinnately lobed" 14 14 "Fertile flowers 1--2 per head" "Crupina {Crupina vulgaris}" 14 "Fertile flowers many per head" 15 15 "Leaf spiny" "Centaurea benedicta" 15 "Leaf not spiny" 16 16 "Pappus of awns with reflexed barbs; phyllaries in 2 series, unarmed" Bidens 16 "Pappus 0 or of smooth or minutely rough bristles or narrow scales; phyllaries graduated in 5+ series, often fringed or spine-tipped" 17 17 "Distal phyllary margin expanded as a spiny-margined, fringed, or irregularly toothed appendage" Centaurea 17 "Distal phyllary margin entire, tapered smoothly to +- flattened spine at tip" "Volutaria canariensis" 18 "Phyllaries (or outermost bracts of head) papery, membranous,+ or scarious, sometimes green only in proximal 1/2 or in narrow, central band; heads often embedded in woolly hairs" 19 18 "Phyllaries generally green (+- purple) throughout, sometimes scarious-margined or inner scarious throughout; heads generally not embedded in woolly hairs" 33 19 "Phyllaries 0 or 1--6, not overlapping, < flowers; outer receptacle paleate; some or all pistillate flowers individually subtended by paleae (which often resemble phyllaries)" 20 19 "Phyllaries generally many, overlapping, inner often >= flowers; receptacle epaleate; pistillate flowers not subtended by bracts" 26 20 "Disk flowers bisexual, pappus generally of 13--28+ bristles, +- exserted; inner pistillate flowers with pappus" 21 20 "Disk flowers staminate, pappus 0 or 1--12 bristles, included; pistillate flower pappus 0" 22 21 "Receptacle +- cylindric, height 5--15 × diam; most pistillate paleae open to folded around pistillate flowers, but not enclosing them, acuminate or bristle-tipped; innermost paleae erect or ascending in fruit; outer fruit +- = inner" "Filago {Filago pyramidata var. pyramidata}" 21 "Receptacle mushroom-shaped to obovoid, length 0.4--15 × width; most pistillate paleae +- enclosing pistillate flowers, obtuse to acute; innermost paleae spreading in fruit; outer fruit > inner" Logfia 22 "Paleae subtending disk flowers (disk paleae) enlarged, rigid, +- spreading, very different from scales subtending pistillate flowers (pistillate paleae)" 23 22 "Disk paleae 0 or scales +- gradually reduced, scarious, erect" 24 23 "Disk palea tips strongly incurved to hooked inward, acuminate or abruptly pointed, often spine-like; pistillate paleae closed, strongly 3-veined or middle vein obscure, tips generally strongly scarious-winged; receptacle not bristly, generally widest at tip" Ancistrocarphus 23 "Disk palea tips erect or spreading, +- flat to folded, not spine-like, obtuse; pistillate paleae open, concave, veins obscure, tips not or barely scarious-winged; receptacle bristly, widest at base" Hesperevax 24 "Leaves generally opposite; paleae net-veined, inner edge with scarious wing that is hidden in head; pappus 0" Psilocarphus 24 "Leaves alternate or seeming whorled; paleae parallel-veined, scarious wing visible in head; pappus 0 or generally of 1--12 bristles" 25 25 "Phyllaries 4--6, equal, scarious, obovate, rounded, abruptly different from paleae; style on inner edge of fruit; receptacle length +- 1--2 × width" Micropus 25 "Phyllaries 0 or 1--4, unequal, vestigial or +- like paleae; style +- at fruit tip; receptacle length +- 3--8 × width" Stylocline 26 "Pappus 0 or a minute crown" Artemisia 26 "Pappus of bristles" 27 27 "Herbage short-appressed-hairy, glandular, or silky; distal 1/2 of outer phyllaries leathery, scarious margin 0 or narrow" Pluchea 27 "Herbage +- long-hairy (leaf generally densely woolly abaxially); phyllaries thin, membranous, margin scarious distal to middle or throughout, generally wide" 28 28 "Shrub or subshrub; stem slender, much-branched" "Plecostachys {Plecostachys serpyllifolia}" 28 "Herb (if subshrub, stem erect or ascending)" 29 29 "Plant with creeping rhizome" "Anaphalis {Anaphalis margaritacea}" 29 "Plant taprooted, fibrous-rooted (sometimes from leafy stolons), or with caudex" 30 30 "Heads generally in tight groups in generally spike- or narrow, panicle-like cluster (reduced to terminal cluster in small plants); pappus bristles fused at base, falling in ring" Gamochaeta 30 "Heads in axillary or terminal head-like clusters or in +- open, flat-topped to panicle-like clusters; pappus bristles free or +- fused at base and falling in groups" 31 31 "Heads in dense, hemispheric to +- spheric terminal cluster closely subtended by involucre-like ring of leafy bracts, sometimes also in head-like axillary clusters" Euchiton 31 "Heads in axillary clusters or terminal clusters, not closely subtended by involucre-like cluster of leafy bracts" 32 32 "Annual, 1--30 cm, low-growing; stems generally prostrate or spreading; head clusters +- sessile, axillary or terminal; drying mud, shorelines, other moist habitats" "Gnaphalium {Gnaphalium palustre}" 32 "Annual to perennial herb, 15--200 cm; stems generally erect or ascending, head clusters generally terminal, sessile to stalked, often branched; generally dry habitats" Pseudognaphalium 33 "Pappus well developed" 34 33 "Pappus 0 or reduced to a minute crown" 48 34 "Pappus of flattened scales or barbed awns" 35 34 "Pappus of bristles" 38 35 "Leaves generally opposite throughout (occasionally distal-most alternate)" Lasthenia 35 "Leaves mostly alternate, sometimes very crowded" 36 36 "Plant dotted with sessile resin glands; fruit 3--4-angled" "Amblyopappus {Amblyopappus pusillus}" 36 "Plant densely woolly; fruit compressed" 37 37 "Leaves entire; pappus scales 2; plant densely tufted; GB" "Eatonella {Eatonella nivea}" 37 "Leaves generally wavy-dentate or shallowly lobed; pappus scales 2--7; plant not densely tufted; s SnJV" "Monolopia congdonii" 38 "Main phyllaries in 1 series, equal" Senecio 38 "Main phyllaries in 2+ series" 39 39 "Subshrub or shrub" 40 39 "Annual or perennial herb" 42 40 "Stems +- leafless; receptacle paleate; pappus bristles plumose" "Bebbia {Bebbia juncea var. aspera}" 40 "Stems evidently leafy; receptacle epaleate; pappus bristles +- smooth to barbed" 41 41 "Corolla yellow or becoming +- red-purple; leaves generally +- toothed; pistillate flowers 5--18" Hazardia 41 "Corolla pink to deep rose; leaves entire; pistillate flowers many" "Pluchea sericea" 42 "Stem thread-like; pistillate flowers 1--5" Pentachaeta 42 "Stem stouter; pistillate flowers several to many" 43 43 "Pappus bristles 1--2; leaf palmately lobed or toothed" "Perityle emoryi" 43 "Pappus bristles generally many; leaf entire to pinnately lobed" 44 44 "Head +- flat, button-like" Erigeron 44 "Head generally cylindric, bell-shaped, or +- obconic" 45 45 "Disk flower corolla purple; herbage strongly scented; anther bases short-tailed" Pluchea 45 "Disk flower corolla cream or yellow; herbage not strongly scented; anther bases not tailed" 46 46 "Disk corolla 9--13 mm" "Pyrrocoma carthamoides var. cusickii" 46 "Disk corolla 3--5 mm" 47 47 "Leaf not clasping, entire, toothed, or shallowly few-lobed" Erigeron 47 "Leaf clasping, regularly dentate or spreading-lobed" "Laennecia {Laennecia coulteri}" 48 "Phyllary margins widely scarious or transparent" 49 48 "Phyllary margins generally not scarious or transparent" 52 49 "Delicate annual; pistillate corollas thread-like" Pentachaeta 49 "Perennial herb or stout annual; pistillate corollas short, wider than thread-like" 50 50 "Heads in spikes, racemes, or panicles" Artemisia 50 "Heads 1 or few to many in +- flat-topped clusters" 51 51 "Involucre generally 3--5 mm diam, phyllaries generally 12--20; pappus 0" Sphaeromeria 51 "Involucre 5--22 mm diam, phyllaries generally 30--60; pappus crown-like, 0.1--0.5+ mm" Tanacetum 52 "Ovary of disk flower much reduced; style tip truncate or tack-shaped" 53 52 "Ovary of disk flower well developed; style tip +- branched" 56 53 "Leaf ovate to widely triangular, generally +- basal or proximal cauline, green adaxially, white abaxially; inflorescence open; corolla white; fruit bearing stalked glands" "Adenocaulon {Adenocaulon bicolor}" 53 "Leaf linear to (ob)ovate or +- round, basal and cauline or all cauline, faces +- alike, generally green to gray on 1 or both faces; inflorescence +- dense; corolla +- pale yellow, yellow-white, or +- pink; fruit not glandular" 54 54 "Anthers fused" Artemisia 54 "Anthers +- free or only weakly fused" 55 55 "Annual; leaf 1--2-pinnately divided" "Euphrosyne nevadensis" 55 "Perennial herb or subshrub; leaf generally entire" Iva 56 "Leaf wide, palmately lobed or toothed" "Perityle emoryi" 56 "Leaf linear to narrowly oblanceolate, entire or pinnately toothed to lobed" 57 57 "Plant not glandular, not strongly scented" 58 57 "Plant glandular, +- strongly scented" 59 58 "Leaves opposite" "Lasthenia microglossa" 58 "Leaves alternate" Pentachaeta 59 "Pappus present" "Amblyopappus {Amblyopappus pusillus}" 59 "Pappus 0" 60 60 "Fruit of pistillate flower compressed front-to-back" "Hemizonella {Hemizonella minima}" 60 "Fruit of pistillate flower compressed side-to-side or +- 3-angled in ×-section" Madia