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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.

 

XANTHIUM

Bruce G. Baldwin, adapted from Strother (2006)


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. 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 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 flower: 2: corolla 0, style tips linear, exserted. Staminate flower: 20–150+; corolla ± funnel-shaped, ± white, lobes 4–5, erect or reflexed, filaments fused, anthers free or weakly fused; style tip undivided. Fruit: fusiform, black, enclosed in obovoid to ellipsoid, 2-chambered bur; pappus 0.
2–3 species: ± worldwide; native to New World. (Greek: yellow, from fruit-extract dye) [Strother 2006 FNANM 21:19–20]

Key to Xanthium

1. Nodal spines present, generally 3-lobed, 15–30+ mm, golden; leaf blade ± lanceolate to ovate or lance-linear, abaxially densely strigose, gray to white ..... X. spinosum

1' Nodal spines 0; leaf blade nearly round to ± pentagonal or deltate, abaxially minutely coarse-hairy, green ..... X. strumarium

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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