Tanbark-oak Notholithocarpus densiflorus

 Tanoak is a medium-sized, broadleaf evergreen tree or shrub that measures 20 to 80 feet tall and up to 50 feet wide. It has a conical to a rounded shape with large horizontal branches. The Dwarf Tanoak is a shrub and is usually less than 10 feet tall. The leaves are thick, leathery, and light green. The flowers consist of male catkins that are erect, white, and then turn rust-colored. The female flowers are found at the base of the catkins. The flowers can be so dense that they hid the foliage. The fruit is an acorn that takes two years to mature. This tree is a member of the Fagaceae family which includes beeches, chestnuts, and oaks.

It is native to southwest Oregon and California. These trees are typically found along the Pacific Coast, in the Cascade Mountains and the Klamath Mountains, and down into southern California. It is the only member of this genus native to North America. All other members are native to southeast Asia and Indo-Malaysia.

The Tanoak was formerly in the genus known as Lithocarpus, but it now is a member of the genus Notholithocarpus. Lithocarpus originated from the Greek word, lithos, meaning "rock" and karpos, meaning "fruit."  Notho is Latin and means "false." This references the acorn fruits. The species name, densiflorus, means "densely flowered." It is commonly known as Tanoak or Tanbark-oak, but it is not a true oak even though it produces acorns. 

The Tanoak prefers full sun to partial shade. It performs best in rich, moist soils and mild temperatures. Once established, it is somewhat drought tolerant. It is hardy to USDA Zone 7.  It is wind pollinated and propagated by seeds and sprouts. 

The bark is reddish-brown, moderately thick, and has furrows and ridges. The leaves are simple, alternate, and persist for 3 to 4 years. Leaf fall occurs at the same time as acorn drop. The flowers look similar to those of a chestnut tree, and the fruits look similar to the acorns of an oak tree. 

The Tanoak tree provides shelter and food for mammals and birds and attracts butterflies and moths. The Tanoak bark was once a main commercial source of tannin. Northern California was once the main producer of high-quality leather. Once the tree was stripped of its bark, the tree was of little value.  It is now being devastated by a disease known as sudden oak death.

Seasons of Interest:

Bloom:  Spring and Summer                  Foliage: Year-round, leaf drop every 3 to 4 years            Fruits: Fall, matures every 2 years       Bark:  Year-round

Quick ID Hints:

• broadleaf evergreen, moderate size conical or rounded shape
• reddish-brown thick bark with furrows and ridges
• stout, rounded, reddish-brown stems that are densely hairy when young
• densely flowered in spring and summer with erect male catkin measuring 2 to 4 inches long, white, and then rust-colored
• female flower is at the base of the catkin and is greenish-yellow
• 1-inch long acorns that may be single or paired with shallow caps and dense bristles, take 2 years to mature

Insects, Diseases, and Other Plant Problems: Tanoaks are fairly resistant to insects, but oak worms may feed on the foliage. Up until the mid-1990s, this tree was mostly disease-free. However, this species has been become seriously affected by Sudden Oak Death. Spores are produced on the foliage that infects the trunk of the tree then resulting in the death of the tree. Unfortunately, this also results in the loss of habitat, shelter, and food for wildlife.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University