New York Metropolitan Flora

Common Names

White Poplar, Silver Poplar

Field Identification

Tree with simple, opposite leaves; leaves with dense white hairs beneath.

Other uses

The use of poplars for removal and sequesterization of various heavy metals and other chemicals from contaminated soils (phytoremediation) has been explored.

Also poplars might be useful as biomonitors of heavy metal air pollution (Sawidis et al, 1995).

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Stories

Populus alba was introduced into the United States in 1784 from Europe where it has long been cultivated as a landscape and street tree—both in rural and urban areas. From these early introductions it has naturalized throughout the country.

Nomenclature

Populus alba L., Sp. Pl. 1034. 1753.

Populus major Mill., Gard. Dict. ed. 8, P. no. 4. 1768.

Populus alba genuina argentea Wesmael in De Candolle, Prodr. 16,2: 324. 1868.

TYPE: unknown

Description

HABIT Perennial, deciduous, phanerophytic, tree, diclinous and dioecious, up to 30 m tall.

STEMS Main stems erect, round. Bark smooth, greenish-white to light gray, later developing numerous lenticels which enlarge and develop into shallow dark splits and ridges, not exfoliating. Branches erect or ascending. Twigs brown to reddish brown or gray, not odoriferous, terete, 1.5-5 mm in diameter, smooth, with appressed, white or light gray tomentum, moderately dense or dense, distributed throughout, glabrescent or not glabrescent, eglandular. Pith brown (occasionally white?), 5-pointed, continuous, nodal diaphragm absent. Sap translucent. For a micro-anatomical study of the xylem see Gol'Traf, 1982 (In Russian). For a synopsis of the root system see Stettler et al, 1996. Roots able to form ectomycorrhizal associations. (Vozzo & Hacskaylo, 1974).

BUDS Terminal and axillary present, monomorphic, scattered along stem; pointed; axillary buds 1 per axil, ovoid, pointed. Bud scales brown, imbricate, chartaceous, with appressed, white or light gray tomentum, moderately dense or dense, distrubted throughout, eglandular. Bud scale scars not encircling the stem. Leaf scars crescent-shaped. Vascular bundle scars 3, crescent-shaped.

LEAVES Alternate, simple, 1 per node, (sometimes appearing opposite/whorled on short shoots), spiral, spaced somewhat evenly along and divergent from stem. Stipules present, caducous, lateral, free from the petiole, small leaf-like. Leaves petiolate, petiole mostly terete, 1-6 cm long, with appressed white-light gray tomentum, sparse to dense, distributed throughout, not glabrescent, eglandular. For a study of the structure and growth of the petioles see Pautov, 1992 (In Russian). Leaf blades: abaxial surface green, adaxial surface green (beneath white-gray tomentum), elliptic to widely elliptic or ovate to widely ovate, bilaterally symmetric, 3-12 cm long, 3-11 cm wide, chartaceous, base truncate or sub-cordate or rounded, margin toothed, serrate or dentate, and sometimes palmately 3-5(7) symmetrically lobed (lobes 1/4 - 1/2 the distance to the midvein, with sinuses rounded or acute; occasionally maple-like shape), apex acute or obtuse, abaxial surface with appressed, white or light gray tomentum, moderately dense to dense, distributed throughout, eglandular. Adaxial surface glabrous or with appressed, white or light gray tomentum, sparse to moderately dense, distributed throughout, eglandular. For an overview of the micro-anatomy of the lower epidermis see Pautov et al., 2002 (In Russian). For an overview of the secondary tissues see Stettler et al, 1996.

FEMALE INFLORESCENCES Precocious, formed on last season's growth, unisexual, axillary raceme, pendant, yellowish, catkin-like; about 5 cm long, up to 12 cm long in fruit. Peduncle and rachis present, hairy. Bracts 1, subtending each flower, petiolate, adnate to pedicel, apices erose and ciliate, lateral surfaces glabrous and eglandular. Pedicels 1-1.5 mm long, with long and unbranched hairs, hairs appressed or spreading, white or light gray, moderately dense, distributed throughout, eglandular.

FEMALE FLOWERS Perianth parts indistinguishable from one another, fragrance absent. Perianth of one whorl, gynoecium set on perianth which is a persistent, glabrous infundibuliform disk composed of connate tepals (perigon). Carpels 2. Locules 1. Stigmas 2, bifid. For development, cytochemistry, and ultrastructure of the stigmas see Li et al, 1995. Styles 1. Ovary superior, ovoid, glabrous, eglandular. Placentation parietal.

MALE INFLORESCENCES Precocious, formed on last season's growth, unisexual, axillary raceme, pendant, yellowish, catkin-like; about 5 cm long. Peduncle and rachis present, hairy. Bract 1, subtending each flower, petiolate, adnate to pedicel, apices erose and ciliate, lateral surfaces glabrous and eglandular. Pedicels 1-1.5 mm long, with long and unbranched hairs, eglandular.

MALE FLOWERS Perianth parts indistinguishable from one another, fragrance absent. Perianth of one whorl, androecium set on perianth which is a persistent, glabrous, infundibuliform disk composed of connate tepals (perigon). Stamens 5-25, exserted. Anthers dehisce longitudinally along the long axis, glabrous, eglandular. Filaments free, straight, glabrous, eglandular.

FRUITS Loculicidal 2-valved capsule, brown, ovoid, 3-7.5 mm long, 1.5-2 mm wide, glabrous, eglandular.

SEEDS Glabrous, eglandular, minute. Adnate tufts of longer "cotton" (which facilitate anemochory) composed of epidermal hairs of the placenta; endosperm completely consumed by developing embryo so that none remains in the mature seed (Nagaraj, 1952).

Habitat

Roadsides, fields, forest edges.

Distribution

Indigenous to Eurasia, widely naturalized throughout North America.

United States -- AR, CA, CT, DC, DE, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WI, WV, WY

Canada -- AB, BC, MB, NB, NF, NS, ON, PE, QC

New York Metropolitan Region -- Nonnative, naturalized throughout the metropolitan region, especially near the coast.

Rarity Status

Global Heritage rank -- G5

Species Biology

Flowering

April [week 1] - May [week 1]

 

Pollination

Anemophily

 

Fruiting

May [week 2] – June (August [week 4])

 

Dispersal

Anemochory

 

Germination

It is difficult to define germination with the small seeds of Populus species; for most species; germinated seedlings should have well-developed hypocotyl hairs, regular growth, and a geotropic response. Seeds that have been dried for storage may suffer injury from rapid imbibition; aeration with humid air after storage has been used to solve this problem. The critical factor for germination is moisture. Young & Young, 1992

The time of ripening is quite variable; a safe criterion for time of fruit collection is when a small percentage of the capsules are beginning to open. Pre-strorage drying immediately after collecting is essential for successful storage. A moisture content of 5-8% improves viability and germination of stored seed. After air drying for 4 days store in a sealed container at 41d F. The critical factor for germination is moisture. (Dirr & Heuser, 1987) Long term viability can be maintained with temperatures below freezing in a dry atmosphere. (Stettler et al, 1996).

Populus alba hybridizes naturally with P. tremuloides (Howard, 1996), P. grandidentata, and P. deltoides.