15. Quercus alba L. (white oak)
Pl. 416 h–j; Map
1853
Plants trees to
35 m tall. Bark light ashy gray, divided into loose plates or strips, or more
or less persistent ridges on old trunks. Twigs 1.5–3.0(–4.0) mm thick, reddish
brown to grayish brown, sometimes glaucous, glabrous. Buds 2–5 mm long, reddish
brown, the scales glabrous or sparsely pubescent, usually also hairy along the
margins. Petioles 6–25 mm long. Leaf blades 12.5–21.0 cm long, 9.5–13.0 cm
wide, relatively thin and flexible, obtuse to somewhat tapered at the base,
divided (30–)60–90% of the width, the lobes (2)3–6 per side, deeper above the
leaf base; well-developed lobes 13–36 mm wide, elliptic to narrowly oblong,
rounded or rounded-obtuse apically, the largest lobes often with 1 or 2 small
secondary lobes on the lower margin and sometimes 1 on the upper margin;
secondary veins (3)4–6 per side, some reaching the margin at the tips of the
lobes, usually others reaching toward sinuses and turning aside before reaching
the margin; the upper surface dull, glabrous, the undersurface more or less
glaucous, appearing glabrous (few to many appressed unbranched hairs visible at
high magnification), smooth to the touch. Acorn stalks 2–41 mm long, the cups
7–12 mm long, 11–23 mm wide, covering 20–40% of the nut, bowl-shaped, the outer
surface with the scales 1.5–3.0 mm long, those near the cup margin not
differentiated. Nuts 16–23 mm long, 14–17 mm wide, barrel-shaped to bluntly
ovoid. 2n=24. April–May.
Common nearly
throughout the state (eastern U.S. west to Minnesota, Nebraska, and Texas;
Canada). Bottomland forests, mesic to dry upland forests, bases and tops of
bluffs, banks of streams and rivers, and margins of sinkhole ponds; also
pastures, railroads, and roadsides.
The leaves in Quercus
alba vary a great deal in depth of lobing and width of the lobes (Baranski,
1975). Forms with leaves that are shallowly divided into broad lobes have been
called f. latiloba (Sarg.) E.J. Palmer & Steyerm.
Hardin (1975)
reviewed natural hybridization in this species. Hybrids with eleven other
species of white oaks are known from throughout its range. Five of these have
been documented from Missouri.