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John O. Sawyer, Jr., except as noted

Shrub, tree; dioecious (monoecious). Stem: trunk < 40 m; wood soft; bark smooth, bitter; buds scaly. Leaf: simple, alternate, deciduous; stipules generally present, deciduous or not, often large. Inflorescence: catkin [or various, or flowers 1]; each flower subtended by 1 bract. Flower: perianth modified into non-nectariferous, cup- or saucer-shaped structure or reduced to adaxial nectary (rarely also with abaxial nectary, then free or fused into shallow cup). Staminate flower: stamens 2–many. Pistillate flower: pistil 1, ovary superior to 1/2-inferior, chambers generally 2–4, placentas parietal, stigma lobes 2–4. Fruit: berry, drupe, or 2–4-valved capsule. Seed: often with basal tuft of hairs.
58 genera, 1210 species: widespread in tropics, northern temperate, arctic. Now including many genera (e.g., Flacourtia, Idesia, Xylosma) formerly in Flacourtiaceae, at least in part because of presence on leaf margins in both families of salicoid teeth (vein extending to tooth tip). In California (and generally outside California), Populus pollinated by wind, Salix by insects, wind. Hybrids common; identification often difficult. —Scientific Editor: Thomas J. Rosatti.

Key to Salicaceae

Tree. Stem: < 40 m; young bark smooth, pale yellow-green to gray; older bark furrowed, brown to gray; twigs with swellings below leaf scars; winter bud generally resinous, scales > 3. Leaf: juvenile, adult, late-season leaves may differ in size, shape, hairiness; generally glabrous; blade 3–11 cm, elliptic to deltate, veins pinnate or ± palmate, tip generally elongate. Inflorescence: catkin pendent, 3–8 cm; bract cut into narrow segments; flowers sessile; nectary a cup- or saucer-like disk. Flower: perianth modified into non-nectariferous, cup- or saucer-shaped structure. Staminate flower: stamens 8–60. Pistillate flower: style short, stigmas 2–3(4), large, scalloped to 2-lobed. Fruit: spheric to conic; valves 2–3(4), 3–12 mm.
40 species: northern hemisphere. (Latin: name for plants of this genus) [Hamzeh et al. 2006 J Torrey Bot Soc 133:519–527]
Unabridged references: [Hamzeh & Dayanandan 2004 Amer J Bot 91:1398–1408]

Key to Populus

P. trichocarpa Hook. BLACK COTTONWOOD
Tree < 30 m; crown wide. Stem: twigs brown, in age gray; winter buds finely ciliate, very resinous, fragrant when opening. Leaf: petiole 1/3–1/2 blade, abaxially round, adaxially channeled; blade 3–7 cm, narrowly to widely ovate (sometimes lanceolate on suckers, stressed plants), adaxially green, abaxially glaucous, often stained with brown resin, base round to cordate, tip acute to tapered, margin finely scalloped.
2n=38. Scattered. Alluvial bottomland, streamsides; 5–3050 m. California Floristic Province, Great Basin Floristic Province; to Alaska, northern Rocky Mountains, Utah, northern Baja California. [Populus balsamifera L. subsp. trichocarpa (Hook.) Brayshaw] [Cervera et al. 2005 Theor Appl Genet 111:1440–1456] Feb–Apr [Online Interchange]
Unabridged references: [Brayshaw 1965 Canad Field-Naturalist 79:91–95]
Unabridged note: Treatment as separate sp. supported by molecular data (Cervara et al.). Hybrids with Populus fremontii (Populus ×parryi) reported for California. See note under Populus angustifolia.

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora,, accessed on Dec 1 2015
Citation for this treatment: [Author of taxon treatment] 2013. Populus, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on Dec 1 2015

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Geographic subdivisions indicated for the distribution of Populus trichocarpa 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.