SALICACEAE

WILLOW FAMILY

Shrub, tree, generally dioecious (rarely monoecious)
Stem: trunk < 40 m; wood soft; bark smooth, bitter; buds scaly
Leaves simple, alternate, deciduous; stipules generally deciduous, often large
Inflorescence: catkin, generally appearing before leaves; each flower subtended by disk or 1–2 nectary glands and 1 bract
Flower: perianth 0
Staminate flower: stamens 1–many
Pistillate flower: pistil 1, ovary superior, chamber 1, stigma lobes 2–4
Seeds many; hairs fine, white, cottony
Fruit: capsule; valves 2–4
Genera in family: 2 genera, 340 species: generally temp (except Australia, Malay Archipelago) moist places; many cultivated. Hybridization common; identification often difficult. Family description, key to genera by John O. Sawyer, Jr.

POPULUS

POPLAR, COTTONWOOD, ASPEN

John O. Sawyer, Jr.

Tree
Stem: trunk < 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
Leaves generally glabrous (juvenile leaves may differ from adult leaves); blade 3–11 cm, elliptic to triangular, veins pinnate or subpalmate, tip generally elongate
Inflorescence: catkin pendent, 3–8 cm; bract cut into narrow segments; flowers sessile, on a cup- or saucer-like disk
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
Species in genus: 40 species: n hemisphere
Etymology: (Latin: name for plants of this genus)

Native

P. fremontii S. Watson subsp. fremontii

ALAMO or FREMONT COTTONWOOD

Stem: crown wide; trunk < 20 m; twigs yellow, becoming gray, glabrous to hairy; winter buds resinous
Leaf: petiole 1/2 to = blade length, laterally compressed near blade; blade 3–7 cm, deltate, base slightly cordate to flat, tip ± tapered, margin coarsely scalloped, surfaces yellow-green, glabrous to hairy, often stained with milky resin
Ecology: Scattered. Alluvial bottomlands, streamsides
Elevation: < 2000 m.
Bioregional distribution: California (except Modoc Plateau)
Distribution outside California: to c Rocky Mtns, n Mexico
Flowering time: Mar–Apr
Synonyms: var. arizonica (Sarg.) Jeps.; var. macdougalii (Rose) Jeps
[Eckenwalder J Arnold Arbor 58:193–208]
Horticultural information: IRR or WET, SUN: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24; susceptible to mistletoe; INV; STBL.