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Alan T. Whittemore, except as noted

Tree, shrub, [woody vine]. Leaf: opposite [alternate], generally palmately or ternately [pinnately] lobed to compound, deciduous, petioled; stipules 0. Inflorescence: umbel, panicle, or pendent raceme, axillary or terminal. Flower: unisexual or bisexual, radial or ± bilateral; sepals (4)5, free or fused; petals 0, 4, or 5(6); prominent disk between petals and stamens; stamens 5–12, free; ovary superior, chambers 2–3, each 2[1]-ovuled, style short or 0, stigmas 2(3), linear, or 1, unlobed. Fruit: 2(3) 1-seeded mericarps, conspicuously winged, or generally leathery, generally 1[many]-seeded capsule [berry, nut, drupe].
150 genera, 1500 species: ± worldwide. Acer traditionally placed in Aceraceae, Aesculus in Hippocastanaceae. Cupaniopsis anacardioides (A. Rich.) Radlk. possibly naturalizing in southern California. —Scientific Editors: Douglas H. Goldman, Bruce G. Baldwin.
Unabridged references: [Harrington, M.G., K.J. Edwards, S.A. Johnson, M.W. Chase, & P.A. Gadek. 2005. Phylogenetic inference in Sapindaceae sensu lato using plastid matK and rbcL DNA sequences. Syst Bot 30: 366–382.]
Unabridged note: Acer and Aesculus have traditionally been placed in small families (Aceraceae and Hippocastanaceae, respectively). However, virtually all the traits considered characteristic of these two small families are also found in the closely related large family Sapindaceae, and it seems more reasonable to emphasize the close relationship of the whole group by treating it as a single family, rather than maintaining two small segregate families that differ from Sapindaceae in virtually nothing except opposite leaves (Harrington et al. 2005).

Key to Sapindaceae

Shrub, tree; occasionally monoecious. Inflorescence: umbel, panicle, or pendent raceme.
± 130 species: northern hemisphere. (Latin name for Acer campestre) Many species monoecious or dioecious.
Unabridged note: The sexuality of Acer species is complex, with some species described as dioecious or monoecious and many species described as having both unisexual and bisexual flowers on the same tree. However, maple flowers that appear morphologically bisexual may be functionally unisexual, producing functional pollen or ovules but not both. More study of sexuality is needed in our native maples. In some Acer species, fruit may become fully developed even if no seed is set, so that production of morphologically normal fruit is no proof that a plant is reproducing.

Key to Acer

A. negundo L. BOX ELDER
Tree < 20 m; dioecious. Leaf: 1–2-ternate, leaflets 3(9); terminal leaflets 4–11 cm, 3–9 cm wide, toothed, generally 1–2-lobed, abaxial surface green, generally felty, occasionally sparsely pubescent Inflorescence: panicle axillary, pendent, appearing with leaves, flowers 10–250. Flower: petals 0. Fruit: wings spreading 60–90°.
Streamsides, bottomland; < 1800 m. California Floristic Province; United States, southern Canada, southern to South America. [Acer negundo var. arizonicum Sarg.; Acer negundo var. californicum (Torr. & A. Gray) Sarg.; Acer negundo var. interius (Britton) Sarg.] Widely planted, especially Great Central Valley, as ornamental or street tree. Mar–Apr [Online Interchange]
Unabridged note: The indumentum of Acer negundo shows some variation, and the sp. has been divided into several varieties or subspecies based on indumentum differences. Most California specimens have rather dense, velvety, spreading hairs ca. 0.3 mm on the leaves, stems; If recognized taxonomically, such plants assignable to var. californicum (Torr. & A. Gray) Sarg. If recognized taxonomically: occasionally plants with glabrous, glaucous twigs assignable to var. arizonicum Sarg.; plants having twigs canescent with short hairs (± 0.1 mm) assignable to var. interius (Britt.) Sarg. These forms based on hairs are scattered throughout the same geographic area, they intergrade with one another, and they do not appear to be well correlated with any other characters. So the varieties seem unnatural, at least as they are currently circumscribed. Humans have been planting Acer negundo genotypes from eastern United States in California since the middle of the 19th century. Old trees may persist on abandoned homesites, but the extent to which they reproduce themselves or cross with native genotypes in California is unknown. Specimens from Great Basin Floristic Province seem to represent planted trees persisting on old homesites. Acer negundo may be naturalizing at one site in Modoc Co. (Bartholomew 6714, CAS).

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Nov 24 2015
Citation for this treatment: [Author of taxon treatment] 2013. Acer, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Nov 24 2015

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click for enlargement Acer negundo
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2006 Louis-M. Landry

Geographic subdivisions indicated for the distribution of Acer negundo Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
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).

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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.