Oaks of the World

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 Quercus oblongifolia
Author Torr. 1853
Synonyms 
Local namesSonoran blue oak ; Mexican blue oak ; encino mexicano azul;
Range SW U.S.A. (Arizona, SW New-Mexico, W Texas); North of Mecico (Durango, Sonora, Chihuahua, Coahuila); to 1700 m;
Growth habit may reach 15 m, but usually smaller; trunk to 30 cm in diameter;
Leaves

2.5-7 x 1.5-2.5 cm; semi-evergreen; sub-leathery, stiff; oblong to elliptic, sometimes lanceolate or oval; apex obtuse or broadly rounded; base cordate or obtuse, sometimes acute or cuneate; margin undulate, cartilaginous, entire or seldom with some teeth (shortly mucronate or not) near apex; blue-green above, bloomy at first, sometimes slightly floccose near the base of the midrib, soon hairless except at the base of midvein; paler beneath, yellowish green or glaucous, with some scattered stellate hairs, becoming glabrous at maturity except at the base of the midvein; 7-9 branched vein pairs, prominent beneath, slightly raised above; petiole short (2-6 mm), slender, often reddish and tomentose;

Flowers March-May; male catkins 2-4 cm long, bearing more than 10 flowers; pistillate inflorescences 8-15 mm with 1 to 5 flowers sessile or on a pubescent peduncle;
Fruits acorn ovoid 1.2-1.8 cm ; solitary or paired; sessile or on a short peduncle de 4-12 mm long; enclosed 1/3 by cup; cup with scales greyish pubescent, slightly warty; maturing in 1 year from September to November; cotyledons connate; edible;

Bark, twigs and
buds

bark light grey, deeply fissured into small square plates; young twigs 1-1.5 mm thick, at first stellate tomentose, becoming hairless, grey to red brown; older twigs rough, becoming blackish; buds brown, subglobose, 1-3 mm long, scales ciliate on margin; stipules sometimes persistent aroud terminal bud;
Hardiness zone, habitat hardy (hardiness zone 7); all types of soils; withstands hot and dry soils;
Miscellaneous -- A. Camus : n° 180;
-- section Quercus;
-- closely related (or conspecific ?) to
Q.engelmannii, but leaves wider (on average 4.5 x 3 cm, instead of 4 x 1 cm for Q.engelmannii);
-- no hybrids known;
Subspecies and
varieties
 
Pictures