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Description


Annual or perennial herbs, sometimes shrubs or climbers. Leaves alternate or opposite, sometimes whorled, simple or 2 to many foliate, entire or toothed, exstipulated. Inflorescence head or capitulum, surrounded by involucral bracts, sessile or peduncled, homogamous or heterogamous or sometimes monoecious. Flowers actinomorphic or zygomorphic, hermaphrodite, unisexual or neuter, epigynous. Calyx modified to pappus of bristles, awns or scales. Corolla sympetalous, petals 4-5, tubular, ligulate or bilabiate. Anther syngenesious. Ovary unilocular, ovule solitary. Fruit a cypsela or an achene, crowned by the persistent pappus. Seeds exalbuminous.

Key to the Genus

Serial Key Reference
1a. Pappus absent or reduced to a minute ring or bristle 2
1b. Pappus present, distinct 11
2a. Capitula homogamous, female capitula covered with spines and glands Xanthium
2b. Capitula heterogamous 3
3a. Leaves opposite 4
3b. Leaves alternate 6
4a. Capitulum sessile Acanthospermum
4b. Capitulum peduncled 5
5a. Achenes wingless; receptacle flat or convex Wedelia
5b. Achenes ciliate or winged on the margin; receptacle raised conical Spilanthes
6a. Herbs with winged stems; capitula globose clusters or glomerules Sphaeranthus
6b. Herbs without winged stems; capitula not in globose clusters 7
7a. Leaves usually deeply disected-pinnatifid or pinnatisect 8
7b. Leaves entire or toothed 9
8a. Involucral bracts many-seriate Chrysanthemum
8b. Involucral bracts 1-2 seriate Cotula
9a. Erect or prostrate herbs 10
9b. Trees or shrubs Tithonia
10a. Prostrate herbs; capitula sessile Centipeda
10b. Erect herbs; capitula peduncled Calendula
11a. Capitula homogamous 12
11b. Capitula heterogamous 30
12a. Leaves opposite 13
12b. Leaves alternate or radical 19
13a. Flowers pale red; peduncle long, up to 5 cm Hemistepta
13b. Flowers white, light pink or whitish-blue; peduncles short 14
14a. Plants usually scandent or twining herbs; flowers white Mikania
14b. Plants herbs, undershrubs or shrubs; flowers white, light pink or whitish-blue 15
15a. Pappus paleaceous scales; receptacle conical Ageratum
15b. Pappus slender hairs; receptacle flat or convex 16
16a. Bracts biseriate; flowers white or yellow 17
16b. Bracts many seriate; flowers bluish-white 18
17a. Cypsela oblong-obovoid, 3-5 lobed; flowers white Adenostemma
17b. Cypsela narrowly fusiform or linear, tetragonous, truncate or erostrate; flowers yellow Bidens
18a. Stem and branches pubescent; pappus barbed Chromolaena
18b. Stem and branches glabrous; pappus capillary, scabrous Eupatorium
19a. Leaves alternate 20
19b. Leaves radical 26
20a. Pappus copious, feathery, connate at the base into a deciduous ring; bracts spinescent Cirsium
20b. Pappus not copious, feathery, not connate at the base into a deciduous ring; bracts not spinescent 21
21a. Flowers ligulate; leaves semiamplexicaul and auriculate at the base Sonchus
21b. Flowers tubular; leaves not semiamplexicaul and auriculate at the base 22
22a. Involucral bracts 2, keeled or winged; achene ovoid, winged on each side Caesuli
22b. Involucral bracts more than 2, not keeled or winged; fruits wingless 23
23a. Inflorescence terminal, racemose-spicate, heads clustered in the axils of leaf-like bracts; involucral bracts 8, in decussate pairs Pseudoelephantopus
23b. Inflorescence loose terminal corymbose or racemes or panicles; involucral bracts more than 8, not in decussate pairs 24
24a. Involucral bracts uniseriate; corolla brick-red or dark orange Crassocephalum
24b. Involucral bracts several-seriate; corolla white to purplish or pinkish, violet or bluish 25
25a. Heads each subtended by 3-8, foliaceous bracts; pappi caducous Centratherum
25b. Heads not each subtended by foliaceous bracts; pappi persistent Vernonia
26a. Corolla tubular 27
26b. Corolla ligulate 28
27a. Capitula subtended by foliaceous bracts; cypsela 10-11 ribbed Elephantopus
27b. Capitula not subtended by linear-oblong bracts; cypsela angled or 5-ribbed Emilia
28a. Bracts 2-3 seriate 29
28b. Bracts many-seriate 30
29a. Leaves entire or sinuate-toothed; achene usually elliptic or somewhat rounded and angular; pappus smple Ixeris
29b. Leaves sub-pinnatifid or lyrate-pinnatifid; cypsela fusifom, 11-14 ribbed; pappus bristles Youngia
30a. Stem stoloniferous; achenes truncate or tapering and rostrate at the apex Launaea
30b. Stem without stolon; achenes with a prominent beak Lactuca
31a. Plants aromatic Pluchea
31b. Plants not aromatic 32
32a. Leaves radical Gerbera
32b. Leaves cauline, opposite or alternate 33
33a. Leaves opposite 34
33b. Leaves alternate 41
34a. Capitula sessile to subsessile 35
34b. Capitula peduncled 36
35a. Leaves sessile; capitulum subglobose-campanulate; flowers enclosed by the palea Enhydra
35b. Leaves petiolate; capitulum oblong or ovoid; flowers not enclosed by the palea Synedrella
36a. Ray-florets 1-seriate 37
36b. Ray-florets more than 1-seriate 39
37a. Ray-florets female Zinnia
37b. Ray-florets neuter 38
38a. Involucre sub-hemispheric; pappus 2-4, barbellate awns, persistent Cosmos
38b. Involucre wide campanulate; pappus 2, arsitate, caducous Helianthus
39a. Branches leafy, herbaceous; bracts 1-seriate; leaves gland-dotted Tagetes
39b. Branches not leafy, hard/ subherbaceous; bracts more than 1-seriate; leaves without gland-dotted 40
40a. Flowers whitish-yellow or yellow; cypsela silky villous; pappus plumose Tridax
40b. Flowers pure white; cypsela glabrous; pappus weak teeth or bristles Eclipta
41a. Leaves quite entire; hoary or wooly herbs Gnaphalium
41b. Leaves serrate, dentate or pinnatifid 42
42a. Prostrate or suberect herbs; leaves sessile, sinuate-pinnatifid Grangea
42b. Erect herbs or undershrubs; leaves sessile or petioled 43
43a. Plants aromatic 44
43b. Plants not aromatic 45
44a. Anther base sagittate, tailed; pappus slender, often caducous Blumea
44b. Anther base faintly sagittate or obtuse, not tailed; pappus persistent Laggera
45a. Ray or outer florets 1-2 seriate 46
45b. Ray or outer florets multiseriate 47
46a. Pappus 1-seriate; pubescent, villous herbs; stem not leafy Aster
46b. Pappus 2-seriate; woolly or villous herbs; stem not leafy Pulicaria
47a. Capitula globose clusters on dichotomous cymes; petals of female florets absent Thespis
47b. Capitula disciform on corymbose or panicles; petals of female florets present 48
48a. Leaves semi-amplexicaul; anther base sagittae; pappus copious Blumeopsis
48b. Leaves sessile or short petioled; anther base obtuse-enire; pappus setose-scabrous Conyza