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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.


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

1. Leaf compound, leaflets stalked; inflorescence axillary, pendent panicle ..... A. negundo

1' Leaf simple, palmately lobed, or compound with leaflets sessile; inflorescence not a pendent panicle

2. Abaxial leaf surface white or ± white-green; flowers present before leaves, in dense clusters; petals 0 ..... A. saccharinum

2' Abaxial leaf surface green; flowers present with leaves, inflorescence cyme, raceme, or panicle; petals present

3. Leaf lobes 7–9 ..... A. circinatum

3' Leaf lobes 3–5

4. Leaf 10–25 cm wide; inflorescence pendent, flowers 20–90 ..... A. macrophyllum

4' Leaf 1.4–10 cm wide; inflorescence ascending, flowers 2–30

5. At least leaf veins, margins pubescent; each lobe with 0–1(2), large, rounded teeth per side; fruit wings widely spreading 160–200° ..... [A. campestre]

5' Leaf glabrous; each lobe with 3–many, small, sharp teeth per side; fruit wings overlapping or spreading (40)70–120° ..... A. glabrum

6. Petiole 0.9–2.4 cm, blade 1.4–2.8 cm, 2–3.5 cm wide; lobes rounded or obtuse, lateral lobes with 3–7 obtuse to acute teeth on outer side ..... var. diffusum

6' Petiole 2.8–9.7 cm, blade 2.9–5.6 cm, 3.6–6.3 cm wide; lobes acute, lateral lobes with 5–22 acute to apiculate teeth on outer side ..... var. glabrum


Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, [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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