Dwarf Tanoak

Tanoak (Notholithocarpus densiflora) can grow in two forms: a tree (var densiflora) or a shrub (var echinoides). In July, Leonard and I found dwarf tanoak (also called tanoak shrub) growing in profusion along the Castle Lake Road in Shasta Trinity National Forest (Siskiyou County CA).

A member of the Beech/Oak Family (Fagaceae), dwarf tanoak is a native, endemic to Southwestern Oregon and California. Very shade tolerant, dwarf tanoak grows in forests, woodlands and chaparral with fertile soils and summer moisture below about 6,500′.

The shrub form of tanoak has a broad, spreading crown that can grow to about 10 feet in height. The evergreen leaves are persistent for about 3 to 4 years. The leaf margins are entire to wavy or few-toothed. The upper leaf surface is dark green while the lower blade is light green. Although the leaf is densely covered with white pubescence when young, the upper surface becomes almost glabrous (lacking hairs) with age while the lower surface remains hairy. The parallel leaf veins are less prominent in the shrub growth form.

Dwarf tanoak flowers are unisexual and both pollinate and seed catkins occur on the same plant. Male catkins are upright with long stamens. The tiny, solitary female flowers are located at the base of the male flowers.

The fruits, yellowish-brown acorns, mature in the autumn of the second year. Acorns occur singly or in pairs and have shallow cups covered with bristly scales.

Tanoak acorns were a staple in the diets of some Native Americans. The acorns would be ground then washed in hot water to remove bitter tannins. The resulting meal could be made into breads and mush. Wildlife also eats dwarf tanoak acorns and young shoots.

Over time, dwarf tanoak has been classified in various genera. Recently Lithocarpus densiflora var echinoides was the accepted designation, however, currently the genus is Notholithocarpus. The genus name means “false Lithocarpus” (notho is false in Greek). Lithocarpus also comes from Greek (“lithos”/rock and “karpos”/fruit thus rock fruit) and refers to the acorns. The species designation means “densely flowered”, as in the male catkins, while the variety, echinoides, may refer to the acorn scales (“spiny” or “looking like a hedgehog”).

I will present more about the tree form of tanoak, and tanoaks in general, in a future post.

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1 Response to Dwarf Tanoak

  1. tonytomeo says:

    Ew! Interesting, but I am none too keen on the tanoak anyway. A dwarf form sounds compelling, but not something I would want in the landscape here . . . although, it might be an unusual option to the trees. Tanoak is VERY susceptible to SODS, and is blamed by some for spreading the disease to the more desirable coast live oaks. They are in a weird situation now, in which infested trees do not die so suddenly. After getting infected with the Phytophthora ramorum, they do not necessarily become infested with the ambrosia beetles that kill them. Some have lived with the disease for a few years.

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