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Vascular Plants of California
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Acer glabrum var. glabrum

Higher Taxonomy
Family: SapindaceaeView DescriptionDichotomous Key
Habit: 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].
Genera In Family: 150 genera, 1500 species: +- worldwide. Note: Acer traditionally placed in Aceraceae, Aesculus in Hippocastanaceae. Cupaniopsis anacardioides (A. Rich.) Radlk. possibly naturalizing in southern California.
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).
eFlora Treatment Author: Alan T. Whittemore, except as noted
Scientific Editor: Douglas H. Goldman, Bruce G. Baldwin.
Genus: AcerView DescriptionDichotomous Key

Common Name: MAPLE
Habit: Shrub, tree; occasionally monoecious. Inflorescence: umbel, panicle, or pendent raceme.
Etymology: (Latin name for Acer campestre) Note: 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.
Species: Acer glabrumView Description 

Habit: Shrub, small tree, < 6 m; dioecious (or staminate plant with some bisexual flowers). Leaf: 3-lobed (or 3 sessile leaflets) 1/4--3/4(1) of leaf length, at least outer side toothed, teeth 3--22, acute to obtuse; abaxial surface pale green, glabrous. Inflorescence: terminal, ascending, flowers 3--8, appearing after leaves. Flower: petals 2--3 mm, +- = sepals. Fruit: wings spreading (0)70--120°, rarely touching, parallel.

Unabridged Note: Acer glabrum is a very variable sp., but the pattern of variation is confusing. The species has been divided into as many as six varieties, but most of the variation probably results from local selection and clinal variation, not divergence that can be recognized taxonomically. Justice (1995, 2002) follows some earlier authors in restricting the name Acer glabrum var. glabrum to Rocky Mountain populations, and separating populations from California and southern Oregon as var. torreyi (Greene) Smiley based on supposed differences in the venation and form of the lobe apex and marginal teeth (var. glabrum with leaf lobes and marginal teeth acute, and fine venation clearly visible and forming regular areoles, and var. torreyi with leaf lobes and marginal teeth usually broad and apically rounded, and fine venation "somewhat obscured" and less regular). I find these characters more variable in both regions than Justice's accounts suggest. There are no constant differences between plants from the two regions, however. Plants from around the type locality in Colorado tend to have short-acuminate lobes and long, sharply acute teeth, but some California specimens approach this morphology (especially from the Klamath region), and California specimens with acute teeth and lobes are fairly common (especially in the Klamath region). Plants from Wyoming, Utah, southeastern Idaho and southernmost Montana generally have blunt teeth and lobes, and are generally indistinguishable from California specimens. Given the variability of these characters and the absence of consistent differences between the named taxa, I see no valid basis for excluding California plants from var. glabrum. Some older references key all plants with compound leaves to var. neomexicanum (Greene) Kearney & Peebles. Compound leaves do occur rarely in California, but these plants are not referable to var. neomexicanum which is found in CO, New Mexico. Justice (1995, 2002) gives characters that define the variety adequately. Acer glabrum var. douglasii (Hook.) Dippel is found from northern and eastern Oregon, southern Idaho, south-central Montana north to southern Alaska. This variety has been reported for California, but all specimens seen named as var. douglasii from southern of Lane County, Oregon have been misidentified. Acer glabrum var. douglasii differs from our California plants as follows:
1. Middle lobe of leaf triangular or triangular-ovate, widest at (or near?) base, strongly slender-acuminate, with many sharp teeth .....-> var. douglasii;
1' Middle lobe of leaf ovate, oblong, rhombic, or obovate, broadened well above its base; apices obtuse, acute, or short-acuminate; teeth few to many, blunt to sharp .....-> varieties diffusum and glabrum;
If recognized taxonomically, plants with mericarp wings overlapping assignable to var. greenei A.C. Keller, reported as endemic to the Inyo Mountains and the eastern side of southern SN but plants with such fruit also occur in KR. Murray (Kalmia 7:1--20. 1976) and Shevock (TJM (1993)) reported that this var. has leaves like those of the so-called var. torreyi [var. glabrum sensu lato, see below], but in fact, this achene form is found on plants with the small, obtuse, few-toothed leaves of var. diffusus and on plants with the large, acute, many-toothed leaves of var. glabrum s. l. Justice (1995, 2002) reports that the character is commonly variable within populations, and the samaras even vary within some specimens; for instance, E. Carter 693 (CAS) from Trinity Co. has some fruit with parallel or connivent wings, while other fruit on the same specimen has wings diverging by angles up to 60°. Since the fruit character is not correlated with any other characters and may be variable within populations or even on a single tree, Justice is surely correct in denying taxonomic status to var. greenei.

Unabridged Reference: Justice, D. 1995. The systematics of Rocky Mountain Maple, Acer glabrum Torr. M.S. thesis, University of British Columbia. Available at [broken 21.vii.2010]; Justice, D. 2002. Leaf shape in Rocky Mountain Maple, Acer glabrum Torr. Menziesia 7(3): 4--6. Available at
Acer glabrum Torr. var. glabrum
Leaf: petiole 2.8--9.7 cm; blade 2.9--5.6 cm, 3.6--6.3 cm wide, thin; lobes acute, outer side toothed, teeth 5--22, acute to abruptly soft-pointed.
Ecology: Moist to +- dry, montane rocky slopes, canyons; Elevation: 1400--3000 m. Bioregional Distribution: KR, NCoRH, CaRH, n&c SNH; Distribution Outside California: to Oregon, Montana, Colorado. Flowering Time: May--Jun
Synonyms: Acer glabrum var. greenei A.C. Keller; Acer glabrum var. torreyi (Greene) Smiley
Jepson eFlora Author: Alan T. Whittemore
Index of California Plant Names (ICPN; linked via the Jepson Online Interchange)

Previous taxon: Acer glabrum var. diffusum
Next taxon: Acer macrophyllum

Botanical illustration including Acer glabrum var. glabrumbotanical illustration including Acer glabrum var. glabrum

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Citation for this treatment: Alan T. Whittemore 2012, Acer glabrum var. glabrum, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on July 22, 2024.

Citation for the whole project: Jepson Flora Project (eds.) 2024, Jepson eFlora,, accessed on July 22, 2024.

Acer glabrum  
var. glabrum
click for image enlargement
©2009 Aaron Schusteff
Acer glabrum  
var. glabrum
click for image enlargement
©1999 Julie Kierstead Nelson
Acer glabrum  
var. glabrum
click for image enlargement
©2011 Barry Breckling
Acer glabrum  
var. glabrum
click for image enlargement
©2015 Barry Breckling
Acer glabrum  
var. glabrum
click for image enlargement
©1999 Julie Kierstead Nelson

More photos of Acer glabrum var. glabrum
in CalPhotos

Geographic subdivisions for Acer glabrum var. glabrum:
KR, NCoRH, CaRH, n&c SNH
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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 occurrence).


Data provided by the participants of the  Consortium of California Herbaria.

View all CCH records
All markers link to CCH specimen records. The original determination is shown in the popup window.
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 Flowering-Fruiting Monthly Counts

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).