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Vascular Plants of California
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Xanthium spinosum

Higher Taxonomy
Family: Asteraceae (Compositae)View DescriptionDichotomous Key
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, Doellingeria, Eurybia, Ionactis, Oreostemma, Sericocarpus, Symphyotrichum; Chamomilla in Matricaria; Bahia in Hymenothrix; 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 Picradeniopsis; Trimorpha in Erigeron; Venidium in Arctotis; Viguiera in Aldama and Bahiopsis; Whitneya in Arnica. Amauriopsis in TJM2 (2012) treated here in Hymenothrix; Arida in Leucosyris; Bahia in Picradeniopsis; Eucephalus in Doellingeria.
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.
Genus: XanthiumView DescriptionDichotomous Key

Common Name: COCKLEBUR
Habit: Annual, coarse, 10--200+ cm. Stem: erect, branched; nodal spines 0 or present. Leaf: generally alternate (proximal 2--6 occasionally opposite), petioled or distal sessile, linear to nearly round, often +- palmately or pinnately lobed, ultimate margins toothed or entire, faces minutely coarse-hairy or +- strigose, generally gland-dotted. Inflorescence: heads unisexual, 1 or clustered in distal axils, or in terminal 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; phyllaries 8 or 0, free, flat; paleae 30--75+ in 6--12+ series, all proximally fused and hardened, tips free, spreading, cylindric or +- conic, stiff, distally +- hooked, distal 1--3 sometimes longer, stouter, sometimes not hooked, together becoming a hard, spiny bur. Staminate Flower: 20--150+; corolla +- funnel-shaped, +- green, lobes 4--5, erect or reflexed, filaments fused, anthers weakly fused at tips or free; 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.
Etymology: (Greek: yellow, from fruit-extract dye) Note: Burs cling readily to fur or fabrics.
eFlora Treatment Author: David J. Keil & Bruce G. Baldwin
Reference: Strother 2006 FNANM 21:19--20; Tomasello 2018 Mol Phylogen Evol 127:135--145
Xanthium spinosum L.
Habit: Plant 10--60(120+) cm; herbage minutely strigose. Leaf: petiole 1--15(25+) mm; blade 4--8(12+) cm, 1--3(5+) cm wide, pinnately veined and often pinnately 3(7+)-lobed, ultimate margin entire or few-toothed. Pistillate Head: Involucre absent. Fruit: bur 10--12(15+) mm. Chromosomes: 2n=36.
Ecology: Disturbed, seasonally wet, often alkaline sites, in grassland, marshes, watercourses; Elevation: < 1875 m. Bioregional Distribution: CA-FP, MP, D (rare); Distribution Outside California: worldwide; probably native to South America. Flowering Time: Jul--Oct
Jepson eFlora Author: David J. Keil & Bruce G. Baldwin
Reference: Strother 2006 FNANM 21:19--20; Tomasello 2018 Mol Phylogen Evol 127:135--145
Index of California Plant Names (ICPN; linked via the Jepson Online Interchange)

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Botanical illustration including Xanthium spinosum

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Citation for this treatment: David J. Keil & Bruce G. Baldwin 2023, Xanthium spinosum, in Jepson Flora Project (eds.) Jepson eFlora, Revision 12,, accessed on March 02, 2024.

Citation for the whole project: Jepson Flora Project (eds.) 2024, Jepson eFlora,, accessed on March 02, 2024.

Xanthium spinosum
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©2008 Neal Kramer
Xanthium spinosum
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©2011 Barry Breckling
Xanthium spinosum
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©2018 Neal Kramer
Xanthium spinosum
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©2018 Neal Kramer
Xanthium spinosum
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©2009 Barry Rice

More photos of Xanthium spinosum
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Geographic subdivisions for Xanthium spinosum:
CA-FP, MP, D (rare)
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map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).


Data provided by the participants of the  Consortium of California Herbaria.
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Blue markers indicate specimens that map to one of the expected Jepson geographic subdivisions (see left map). Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.

CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa, if there are more than 1 infraspecific taxon in CA.
Blue line denotes eFlora flowering time (fruiting time in some monocot genera).