Quercus phellos L. - Willow Oak, Peach Oak, Pin Oak, Swamp Willow Oak

Native , Occasional

By Steven D. Glenn

Not peer reviewed

Last Modified 01/25/2013

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Quercus phellos

The current records from Suffolk County are local escapes from landscape elements.

Common Names

Willow Oak, Peach Oak, Pin Oak, Swamp Willow Oak

Field Identification

A medium sized deciduous tree with tight bark and alternate, simple, entire-margined leaves resembling a willow tree; catkin-like flowers in spring followed by acorns in the fall.

Food uses

Native American often used the acorns for an unspecified food products, usually by removing the tannins by boiling the nuts or soaking them in lye water. (Moerman, 1998)

Medicinal uses

Used by Native Americans to treat aches and pains, and made a decoction to cleanse the body and strengthen the marriage. (Moerman, 1998)

Other uses

Oak-mast surveys may help wildlife agencies better understand dynamics of fall harvests and may be useful in harvest management models that attempt to stabilize fall harvest rates of game animals (Norman, 2003).

Tannins derived from oaks have been used historically to tan animal hides into leather. (Burrows & Tyrl, 2001)

Native American often used the plant to make lye and toy ball sticks.(Moerman, 1998)

Poisonous Properties

Oak leaves, buds, bark, and acorns contain tannins which have varying degrees of toxicity in different animals. Although oak foliage and acorns provide valuable food for many wildlife species and even some livestock, oak toxicosis, a urinary and digestive tract disease can occur when some animals are forced to subsist on oaks exclusively for several days. Poisoning is rare in humans due to the large amounts needed to ingest to cause symptoms. (Burrows & Tyrl, 2001)


Dryads (or "tree spirits") are nymphs associated with Greek mythology which live near, or in, trees. Dryads are born bonded to a specific tree, originally, in the Indo-European Celtic-Druidic culture, an oak tree. Drys in Greek signifies 'oak,' from an Indo-European root *derew(o)- 'tree' or 'wood.'

In a nationwide vote hosted by the National Arbor Day Foundation in 2001, the oak was selected as America's National Tree.


*Quercus phellos L., Sp. Pl. 2: 994. 1753.

?Quercus salicifolia W. Young, Cat. Arb. Arbust. Am. 20. 1783.

Quercus phellos (sylvatica) Michx., Hist. Chenes Am. Sept. no. 7, t. 12. 1801.

*Quercus phellos f. intonsa Fern., Rhodora 44: 392. 1942.


HABIT Perennial, deciduous, phanerophytic, tree, diclinous and monoecious, 20-30 m tall.

STEMS Main stems ascending or erect, round. Bark gray or dark gray, tightly irregularly fissured, not exfoliating. Branches erect or ascending or horizontal. Twigs fluted-terete, 2-4 mm in diameter, smooth and lenticellate. 1st year twigs reddish-brown to brown and sparsely to moderately covered with simple and fasciculate appressed to spreading white to light gray to light brown hairs. 2nd year twigs gray to brown and hairs becoming less dense and turning light gray; 3rd year and older glabrous. Pith white, 5-pointed, continuous, nodal diaphragm absent. Sap translucent. For an anatomical study of the xylem see Tillson & Muller, 1942.

BUDS Terminal and axillary present, clustered at twig apices and scattered along stem. Terminal bud ovoid, semi-pointed; axillary buds ovoid, semi-pointed. Bud scales dark reddish-brown or brown, imbricate, with short and unbranched appressed brown or light brown hairs, sparsely distributed marginally. Bud scale scars encircling the twig. Leaf scars crescent or half-round shaped. Vascular bundle scars numerous, scattered.

LEAVES Alternate, simple, (appearing pseudo-opposite or pseudo-whorled at twig apices), crowded toward stem apex or spaced somewhat evenly along and divergent from stem. Stipules lateral, free from the petiole, linear, caducous. Petiole adaxially flattened, .1-.4 cm long, glabrous or often with light brown to white fasciculate and simple erect to spreading hairs, sparsely to moderately densely distributed throughout. Leaf blades: abaxial surface light green, sometimes glossy; adaxial surface green, sometimes glossy; narrowly elliptic, bilaterally symmetric, 3-12 cm long, 0.8-2.5 cm wide, chartaceous, pinnately veined; base acute or cuneate; margins entire; apex acute and aristate. Abaxial surface papillose and often appearing glabrous with naked eye, but usually exhibits the following hair types: a. fasciculate light brown to white erect to spreading hairs, sparsely to moderately distributed along the main veins; b. simple white to light brown erect to spreading hairs, sparsely to moderately distributed along the main veins; c. tufted multi-radiate light gray to white hairs sparsely distributed throughout (rarely densely distributed throughout- f. intonsa). Adaxial surface essentially glabrous, with all aforementioned hair types when young, occasionally retaining only sparsely scattered minute simple and multi-radiate hairs when mature; (multi-cellular glandular are also reported to occur but none observed in the NYMF area), see Hardin, 1979a;Thompson & Mohlenbrock, 1979; and for an overview of the phenology and the variability and density of hairs due to ecological factors and hybridization see Hardin, 1979b.

FEMALE INFLORESCENCES Coetaneous, spike consisting of a single flower (sometimes 2-3), in axils of current year leaves, subsessile initially, often becoming short-pedunculate in fruit, surrounded by a cupule which is persistent, accrescent, and indurate in fruit (acorn cap). There has been debate over the years regarding the true ontogenetic nature of the cupule. Originally thought to be an involucre of bracts, recent research suggests that the cupule is a complex partial inflorescence derived from stem tissue, see Abbe, 1974;Brett, 1964;Foreman, 1966;MacDonald, 1979;Fey & Endress, 1983. Each cupule subtended by 3 minute, caducous bracteoles.

FEMALE FLOWERS Perianth of one whorl, minute, fragrance absent. Calyx urceolate, of fused sepals. Carpels 3. Locules 3, each containing 2 ovules. Styles 3, each with 1 stigma. Ovary inferior. Placentation axile.

MALE INFLORESCENCES Coetaneous, compound, solitary or fascicled spikes; pendant, catkin-like; in leaf axils of previous year. Rachis moderately covered with brown hairs; elongating with age; with 1 subsessile or sessile flower per node, each flower subtended by a small, sessile caducous bracteole.

MALE FLOWERS Perianth of one whorl, fragrance absent. Calyx actinomorphic, campanulate, of fused sepals. Sepal lobes 3-4, broadly oval to ovate with brown hairs moderately dense distributed throughout. Stamens 3-6, exserted. Anthers glabrous, basifixed, opening along the long axis. Filaments free, 1mm long, straight, glabrous. For a review of pollen morphology see Solomon, 1983a.

FRUITS Acorn (glans (Spjut, 1994)) (calybium (Kaul, 1985)) sessile to short-pedunculate; maturation biennial. Acorn ovoid-subglobose, 1-1.5 cm long, comprised of 2 parts- a. the acetabuliform cup (cupule), enclosing 1/4 to 1/3 of the base of the nut; and b. the nut, 1-seeded by abortion. For a hypothesis that the first ovule fertilized suppresses the normal development of the others see Mogensen, 1975. Cupule exterior composed of imbricate, appressed scales moderately covered with brown tomentum. Nut olive-green to brown, ovoid-subglobose, with large light-colored circular cupule scar at base and apiculate at the distal end, initially with minute short and unbranched appressed light brown to white hairs, sparsely distributed throughout, glabrescent, minutely laterally striate.

One study found a size range of 0.26-1.38 cubic cm with a mean of 0.63 cubic cm and a correlation between smaller acorn size with increasing latitude see Aizen & Woodcock, 1992.

SEEDS Embryo with two large fleshy cotyledons, endosperm lacking. (Young & Young, 1992).


Usually occurring in moist to mesic woods, floodplains, and occasionally in poorly drained upland areas.


Indigenous to the southeastern United States, extending north along the coast to Long Island, New York.

United States -- AL, AR, DC, DE, FL, GA, IL, KY, LA, MD, MO, MS, NC, NJ, NY, OK, PA, SC, TN, TX, VA

New York Metropolitan Region -- Native along the coast from western Long Island to Staten Island and New Jersey.

Rarity Status

Global Heritage Rank -- G5

Connecticut -- Not listed

New Jersey -- Not listed

New York -- S1

Species Biology


April [week4] - May [week 4]




August [week 1] - November [week 2] 

For a study suggesting that masting is effected by weather in conjunction with inherent reproductive cycles see Sork, et al., 1993.



Small predators of acorns facilitate dispersal by dropping undamaged nuts and failing to recover cached nuts. These include Sciurus carolinensis (gray squirrel), Sciurus niger (fox squirrel), Glaucomys volans (Southern Flying Squirrel), Tamias striatus (eastern chipmunk), Peromyscus leucopus (white-footed mouse), Peromyscus maniculatus (deer mouse) and Quiscalus quiscula (common grackle) and Cyanocita cristata (blue jay). (Ivan & Swihart, 2000) (Smith, 1972) (Briggs & Smith, 1989) (Wolff, 1996) (Bosema, 1979) (Darley-Hill & Johnson, 1981) (Johnson & Webb, 1989) (Johnson, et al., 1993)

In addition, one study found that many predators preferred the basal end of the acorn and consumed only 30-60% of the cotyledon. A chemical analyses of acorns from two species revealed that the concentration of protein-precipitable phenolics (primarily tannins) was 12.5% (Q. phellos) and 84.2% (Q. laevis) higher in the apical portion of the seeds where the embryo is located, suggesting that many acorn consumers consistently eat only a portion of the cotyledon of several species of acorns and thereby permit embryo survival. (Steele, et al., 1993).

Probably included in the diet of the grey fox (Urocyon cinereoargenteus) (Scott, 1955), eastern wild turkeys (Meleagris gallopavo silvestris) (Norman, 2003), and white-tailed deer (Odocoileus virginianus) (Bryant, et al., 1996).



Acorns of members of the black/red oak group have embryo dormancy and germinate naturally the following spring, germination is hypogeal. Moist stratification for 30-90 days at 1-5 d C can be used to break dormancy. For germination to occur the moisture content of the acorns must not drop below 20-30%. It is usually impossible to store acorns for more than 6 months.

General rules for collecting and storing acorns: 1. Collect acorns before they lose much water. 2. Ensure acorns are fully hydrated, soak in clean tap water overnight before placing them in storage. 3. Surface dry the acorns just before depositing them in storage to reduce mold growth. 4. Place acorns into cold storage as soon after collection as is possible. (Connor, 2004)

In one study (Q. phellos and Q. laevis), germination experiments revealed equal or greater germination frequencies for partially consumed acorns than for intact acorns. (Steele, et al., 1993).

For a propagation protocol for growing bareroot oaks see Hoss, 2004.