Notholithocarpus densiflorus, commonly known as the Tanoak or Tanbark-oak, is an evergreen tree in the beech family Fagaceae, native to the western United States, in California as far south as the Transverse Ranges, north to southwest Oregon, and east in the Sierra Nevada. It can reach 40 metres (130 ft) tall (though 15–25 metres (49–82 ft) is more usual) in the California Coast Ranges, and can have a trunk diameter of 60–190 centimetres (24–75 in).
Tanbark-oak was recently moved into a new genus, Notholithocarpus, based on multiple lines of evidence. It is clearly not related to the Asian tropical stone oaks, Lithocarpus, but instead is an example of convergent morphological evolution. The North American tanbark-oak is most closely related to the north temperate oaks, Quercus.
The Notholithocarpus densiflorus leaves are alternate, 7–15 centimetres (2.8–5.9 in), with toothed margins and a hard, leathery texture, and persist for 3–4 years. At first they are covered in dense orange-brown scurfy hairs on both sides, but those on the upper surface soon wear off, those on the under surface persisting longer but eventually wearing off too.
The seed is a nut 2–3 centimetres (0.79–1.2 in) long and 2 cm diameter, very similar to an oak acorn, but with a very hard, woody nut shell more like a hazel nut. The nut sits in a cup during its 18-month maturation; the outside surface of the cup is rough with short spines. The nuts are produced in clusters of a few together on a single stem. The nut kernel is very bitter, and is inedible for people without extensive leaching, although squirrels eat them.
Notholithocarpus densiflorus var. echinoides
Members of populations in interior California (in the northern Sierra Nevada) and the Klamath Mountains into southwest Oregon are smaller, rarely exceeding 3 metres (9.8 ft) in height and often shrubby, with smaller leaves, 4–7 centimetres (1.6–2.8 in) long; these are separated as Dwarf Tanoak, Notholithocarpus densiflorus var. echinoides. The variety intergrades with the type in northwest California and southwest Oregon. Tanoak does grow on serpentine soils as a shrub.
Tanoak is one of the species most seriously affected by Sudden Oak Death (Phytophthora ramorum), with high mortality reported over much of the species' range.
Currently the largest known Tanoak specimen is on private timberland near the town of Ophir, Oregon. It has a circumference of 312 inches, about 8.25 feet in diameter at breast height, and is 121 feet tall with an average crown spread of 56 feet.
- ^ Manos, Paul S.; Cannon, Charles H.; Oh, Sang-Hun (2008). "Phylogenetic relationships and taxonomic status of the paleoendemic Fagaceae of Western North America: recognition of a new genus, Notholithocarpus" (PDF). Madrono 55 (3): 181–190. doi:10.3120/0024-9637-55.3.181. http://www.ecologicalevolution.org/content/pdf/Manos09_Notholithocarpus.pdf.
- ^ American Forests
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