Quercus robur L. - English Oak
Non-native , Rare
By Steven D. Glenn
Not peer reviewed
Last Modified 01/25/2013
Common NamesEnglish Oak
Field IdentificationMedium to large deciduous tree with alternate, simple, lobed leaves; with pendant catkin-like flowers in early summer followed by acorns in the fall.
Other usesTannins derived from oaks have been used historically to tan animal hides into leather. (Burrows & Tyrl, 2001)
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 and supposedly 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 primitive times, the Greeks imagined, people were able to live on acorns.
*Quercus robur L. Sp. Pl. 2: 996. 1753.
HABIT Perennial, deciduous, phanerophytic, tree, diclinous and monoecious, 20-25 m tall. Fastigiated forms often encountered in cultivation.
STEMS Main stems ascending or erect, round. Bark light gray or gray, scaly, not exfoliating. Branches erect or ascending. Twigs reddish-brown to dark brown or brown, fluted-terete, 2-5 mm in diameter, smooth and lenticellate, glabrous. Pith white, 5-pointed, continuous, nodal diaphragm absent. Sap translucent.
BUDS Terminal and axillary present, clustered at twig apices and scattered along stem. Terminal bud ovoid, blunt; axillary buds ovoid, blunt. Bud scales reddish-brown to brown, imbricate, essentially glabrous but with short light brown hairs, sparsely distributed marginally. Bud scale scars encircling the twig. Leaf scars half-round-crescent. 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, .2-.6 cm long, glabrous. Leaf blades: abaxial surface light green, adaxial surface green; obovate or narrowly elliptic or oblanceolate, bilaterally symmetric, 4-12 cm long, 2-7 cm wide, chartaceous; base often cordate but occasionally cuneate or obtuse; margins lobed 1/4 - 3/4 the distance to the midvein with lobe apices obtuse, lacking bristle tips; pinnately veined; apex obtuse. Abaxial surface usually glabrous and minutely papillose, sometimes with simple and fasciculate erect or spreading light brown to white hairs, sparsely distributed along midveins. Adaxial surface glabrous.
FEMALE INFLORESCENCES Coetaneous, spike consisting of a single flower (sometimes 2-3), in axils of current year leaves, subsessile initially, becoming 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 elongating with age, with sessile flowers, 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 3-6, eglandular. Stamens (4)6-9(12), exserted, surrounding tuft of brown hairs. Anthers glabrous, basifixed, opening along the long axis. Filaments free, 1mm long, straight, glabrous.
FRUITS Acorn (glans (Spjut, 1994)) (calybium (Kaul, 1985)) pedunculate (peduncle glabrous, eglandular) to 6 cm; maturation annual. Acorn 1.5-3 cm long, comprised of 2 parts- a. the crateriform cup (cupule), enclosing 1/4 to 1/2 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 indurate, imbricate, tightly appressed scales moderately to densely covered with brown to grey tomentum. Nut olive-green to brown, ovoid-oblong, with large light-colored circular cupule scar at base and apiculate at the distal end, essentially smooth (minutely laterally striate), initially with minute short appressed to spreading simple and fasciculate brown or light brown hairs, sparsely distributed apically, glabrescent.
SEEDS Embryo with two large fleshy cotyledons, endosperm lacking. (Young & Young, 1992).
Indigenous to Europe.
New York Metropolitan Region -- Rarely found naturalized in the metropolitan region.
Rarity StatusGlobal Heritage Rank -- G5
July - September
Probably scatter-hoarding by acorn predators Sciurus carolinensis (gray squirrel), Sciurus niger (fox squirrel), based on (Smith, 1972).