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Xanthium

Higher Taxonomy
Family: Asteraceae (Compositae)View DescriptionDichotomous Key

Common Name: SUNFLOWER FAMILY
Habit: Annual to tree. Leaf: basal and/or cauline, alternate, opposite, rarely whorled, simple to 2+ × compound. Inflorescence: 1° inflorescence a head, resembling a flower, of several types (see below), 1--many in generally +- cyme-like cluster; each head generally with +- calyx-like involucre of 1--many series of phyllaries (involucre bracts); receptacle of head flat to conic or columnar, paleate (bearing paleae = receptacle bracts) or epaleate; flowers 1--many per head. Flower: bisexual, unisexual, or sterile, +- small, of several types (see below); calyx 0 or modified into +- persistent pappus of bristles, scales, and/or awns; corolla radial or bilateral (0), lobes generally (0)3--5; stamens 4--5, filaments generally free, generally fused to corolla at tube/throat junction, anthers generally fused into cylinder around style, anther base generally rounded or cordate (deeply sagittate or with tail-like appendages), tip (= flattened appendage) generally projecting beyond pollen sac; pistil 1, 2-carpeled, ovary inferior, 1-chambered, 1-seeded, placenta basal, style 1, tip generally +- 2-branched (except in some staminate disk flowers), branch tips truncate or generally bearing +- brush-like appendages; stigmas 2, generally on adaxial faces of style branches. Fruit: achene (also called a cypsela) (drupe in Chrysanthemoides), cylindric to ovoid, sometimes compressed, generally deciduous with pappus attached.
Genera In Family: +- 1500 genera, 23000 species: worldwide, many habitats. Note: Flower and head types differ in form and sexual condition. A disk flower has a generally radial corolla, with a cylindric tube, expanded throat, and generally 5 lobes. Disk flowers are generally bisexual and fertile but occasionally staminate with reduced ovaries. Discoid heads comprise only disk flowers. A radiant head is a variant of a discoid head, with peripheral disk flower corollas expanded, often bilateral. A ray flower corolla is bilateral, generally with a slender tube and flattened petal-like ray (single lip composed of generally 3 lobes). Ray flowers are generally pistillate or sterile (occasionally lacking styles). Radiate heads have peripheral ray flowers and central disk flowers. Disciform heads superficially resemble discoid heads, with pistillate or sterile flowers that lack rays, together with or separate from disk flowers. A ligulate flower is bisexual, with a bilateral, generally ephemeral corolla and 5-lobed ligule. Liguliflorous heads comprise only ligulate flowers. See glossary p. 31 for illustrations of family characteristics. Echinops sphaerocephalus L., Gaillardia aristata Pursh, Gaillardia pulchella Foug., Hymenothrix loomisii S.F. Blake, Tagetes erecta L., Thelesperma megapotamicum (Spreng.) Kuntze are waifs. Melampodium perfoliatum Kunth, historic urban waif. Ageratum conyzoides L., Guizotia abyssinica (L. f.) Cass., Santolina chamaecyparisus L., orth. var. are rare or uncommon escapes from cultivation. Dyssodia papposa, Ismelia carinata (Schousb.) Sch. Bip. [Chrysanthemum carinatum Schousb.], Mantisalca salmantica (L.) Briq. & Cavill. are historical or extirpated waifs in California. Inula helenium L. not documented in California. Taxa of Aster in TJM (1993) treated here in Almutaster, Eucephalus, Eurybia, Ionactis, Oreostemma, Sericocarpus, Symphyotrichum; Chamomilla in Matricaria; Cnicus in Centaurea; Conyza in Erigeron and Laennecia; Dugaldia in Hymenoxys; Erechtites in Senecio; Hymenoclea in Ambrosia; Lembertia in Monolopia; Osteospermum ecklonis in Dimorphotheca; Picris echioides in Helminthotheca; Prionopsis in Grindelia; Raillardiopsis in Anisocarpus and Carlquistia; Schkuhria multiflora in Bahia; Trimorpha in Erigeron; Venidium in Arctotis; Whitneya in Arnica. Taxa of Arida in TJM2 (2012) treated here in Leucosyris.
Unabridged Note: Largest family of vascular plants in California and of eudicots globally.
eFlora Treatment Author: David J. Keil, except as noted
Scientific Editor: David J. Keil, Bruce G. Baldwin.

Xanthium
Habit: Annual, coarse, 10--200+ cm. Stem: erect, branched; nodal spines present or 0. Leaf: generally alternate (proximal 2--6 occasionally opposite), petioled or distal sessile, linear to nearly round, often +- palmately or pinnately lobed, ultimate margins entire or +- toothed, faces minutely coarse-hairy or +- strigose, generally gland-dotted. Inflorescence: heads unisexual, 1, axillary or in raceme- to spike-like clusters, pistillate generally proximal, staminate generally distal. Staminate Head: 3--5 mm diam; involucre +- saucer-shaped, phyllaries 6--16+ in 1--2+ series, free, +- 1 mm; receptacle conic to columnar, paleae spoon-shaped to wedge-shaped or linear, membranous, distally +- soft-hairy or minutely coarse-hairy. Pistillate Head: 2--5+ mm diam at flower, 6--20+ mm diam in fruit, +- ellipsoid; bracts 30--75+ in 6--12+ series, all proximally fused or outer 5--8 free, tips free, mostly +- hooked except distal 1--3 (generally longer, stouter), together becoming a hard, prickly bur. Staminate Flower: 20--150+; corolla +- funnel-shaped, +- white, lobes 4--5, erect or reflexed, filaments fused, anthers free or weakly fused; style tip undivided. Pistillate Flower: 2: corolla 0, style tips linear, exserted. Fruit: fusiform, black, enclosed in obovoid to ellipsoid, 2-chambered bur; pappus 0.
Species In Genus: 2--3 species: +- worldwide; native to New World. Etymology: (Greek: yellow, from fruit-extract dye)
eFlora Treatment Author: Bruce G. Baldwin, adapted from Strother (2006)
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Key to Xanthium

Previous taxon: Xanthisma spinulosum var. gooddingii
Next taxon: Xanthium spinosum

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Citation for this treatment: Bruce G. Baldwin, adapted from Strother (2006) 2016. Xanthium, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=661, accessed on May 24, 2016.

Citation for the whole project: Jepson Flora Project (eds.) 2016. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on May 24, 2016.


Xanthium strumarium
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© 2013 Neal Kramer
Xanthium spinosum
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© 2009 Barry Rice
Xanthium strumarium
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© 2004 Carol W. Witham
Xanthium strumarium
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© 2013 Neal Kramer
Xanthium strumarium
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© 2003 George W. Hartwell
Xanthium strumarium
click for enlargement
© 2003 George W. Hartwell

More photos of Xanthium in CalPhotos