A shrubby variety of tanoak (L. densiflora var. echinoides) grows near Mount Shasta, on the west slope of the northern Sierra Nevada, in the central Trinity Alps, in the Salmon and Klamath Mountains, and northward through the Siskiyou Mountains into southern Oregon (28).
The shrub variety occupies a narrow elevational band just above that inhabited by the tree form. This variety is found on a wide range of soils including ultrabasics, but generally occurs only on moist sites (27). On deep, productive soils, especially in the Sierra Nevada, it forms a dense cover of large clumps that often become flattened by snow. Stems from such clumps may straggle downslope for 5 m (16 ft) or more. After cutting or burning, upright sprout clumps are formed that closely resemble those of root crown sprouts from tanoak trees in clearcuttings (17).
Small woody plants with slender, deeply toothed leaves were discovered in 1962 on the Challenge Experimental Forest, Yuba County, CA. These plants are believed to be a sublethal recessive mutation of tanoak and have been named Lithocarpus densiflora f. attenuato-dentatus (33).Hybrids
No hybrids of tanoak are known. Although Lithocarpus comprises between 100 and 200 species, all but tanoak are native to southeastern Asia and Indomalaysia (11).