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SALICACEAE WILLOW FAMILY

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

POPULUS COTTONWOOD
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. tremuloides Michx. QUAKING ASPEN
NATIVE
Tree < 15 m; crown slender; highly clonal. Stem: twigs green-white, glabrous; winter buds shiny. Leaf: petiole 2/3 to = blade, laterally compressed; blade 2–4(7) cm, widely ovate to ± round, glabrous, adaxially green, abaxially glaucous, base rounded to cordate, tip tapered, margin finely crenate to serrate.
2n=38. Streamsides, moist openings, slopes in montane, subalpine forest, woodland, sagebrush steppe; 900–3150 m. Klamath Ranges, High North Coast Ranges, Cascade Range, High Sierra Nevada, San Bernardino Mountains, Great Basin Floristic Province; to Alaska, eastern North America, Mexico. Apr–Jun [Online Interchange]

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Next taxon: Populus trichocarpa

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Nov 26 2014
Citation for this treatment: [Author of taxon treatment] 2013. Populus, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=39509, accessed on Nov 26 2014

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Geographic subdivisions indicated for the distribution of Populus tremuloides 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.
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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 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.