Quercus wislizeni A.DC.

Interior Live Oak ranges broadly across California and extends southward into northern Baja California. It is common in the southern Klamath Mountains, the southwestern Cascades, and along the western flank of the Sierra Nevada from Siskiyou County down to Kern County. Scattered populations occur throughout the Coast Ranges, with the species continuing south into the inner Transverse and Peninsular ranges. It occupies a wide variety of upland settings below roughly 1500 m, including lower foothills, river floodplains, and interior valley bottoms. Throughout this distribution, summers are characteristically hot and dry, while winters bring cooler temperatures and reliable moisture, with annual rainfall ranging from about 350 to over 1250 mm. In the past, the species was a dominant tree along the rivers descending the western Sierra Nevada into the Central Valley. Mid-twentieth-century dam construction, however, stabilised flows and made floodplain soils dependably farmable, leading to the removal of most natural stands. Only a handful of large riparian forests remain today. Interior Live Oak continues to be a key species in Blue Oak (Q. douglasii) woodlands, typically accompanying Pinus sabiniana and Aesculus californica. It is also a familiar element of northern mixed evergreen forest, Quercus garryana woodlands, and scrub-oak chaparral, where it often adopts a more shrubby growth form. It has no apparent soil preference, though it is seldom found on serpentine (Pavlik et al. 1991).

Foamy bark canker, a disease affecting mostly Quercus agrifolia, caused by the fungus Geosmithi pallida and spread by the western oak bark beetle, has been found on Q. wislizeni. It was reported in 2016 and again in 2018, and it is assumed that it is widespread in Sierra Nevada around Tuolumne County (Onetto 2016; Foothill-Sierra Pest Control 2018).

What appear to be Quercus wislizeni individuals with golden pubescence on leaf undersides were observed on Palomar Mountain in 2017 (Giseburt 2018). This suggests possible hybridisation with Q. chrysolepis, which would be unusual given that the species are in different sections of the genus. Molecular analysis is underway to attempt to verify this (D. Giseburt, pers. comm. 2025).

Quercus wislizeni was first introduced to the Royal Botanic Gardens, Kew, in 1874, from seed sent by Henry Nicholas Bolander (1831–1897), a German-American botanist and educator who was State Botanist of California from 1864 to 1871. At Kew, Henry found that, in the absence of fruit, it was similar to Q. coccifera, from which he distinguished it by the darker green foliage, longer, pointed buds, and more open habit. The tree proved hardy at Kew but grew slowly, still only 2 m tall in 1897. It reached 4.5 m in 1913, 12 m × 24 cm dbh in 1973 and in 2022 measured 14 m × 38 cm (Elwes & Henry 1910; Bean 1914; The Tree Register 2025). It has grown larger (and faster) in other gardens in the UK: the current champion is at the Sir Harold Hillier Gardens, grown from wild-collected seed and accessioned in 1976, measuring 21.4 m × 62 cm in 2024; a tree at the Royal Botanic Garden Edinburgh, accessioned in 1936 and measuring 12.5 m × 57 cm in 2025, has grown with a leaning trunk and has suffered branch failure (The Tree Register 2025; Royal Botanic Garden Edinburgh 2025).

The US National Champion grows in Calaveras County in northern California, 16.5 m tall, with a trunk 234 cm in diameter, measured in 2019 (National Champion Tree Program 2025). A fine specimen at UC Davis Arboretum in Davis, California, accessioned in 1936, is taller at 18 m × 117 cm in trunk diameter in 2025 (E. Griswold, pers. comm.). The species is found in collections in Europe, as relatively young trees planted in the 1990s or early 2000s.

In Australia, Quercus wislizeni is present in two public arboreta. The best specimens are undoubtedly at Waite Arboretum in Adelaide. The largest were planted in 1954, and as is typical for the species are broader in canopy than they are tall. They are around 10 m tall and around 15–20 m in canopy diameter. Specimens of the shrubby form referred to as var. frutescens are also at Waite, and being planted in 1999, are only about 5 m tall and their canopies about this in diameter (B. & K. Cerlienco, pers. comms. 2025). At the Royal Botanic Gardens Victoria, Melbourne, there are two specimens, the largest accessioned in 1971, about 16 m tall in 2025, and 69 cm in trunk diameter (P. Berbee pers. comm.).

The species was first described by De Candolle (1864), from a specimen sent to him by George Engelmann collected by Dr. Adolphus Wislizenus in 1851 from the American Fork of the Sacramento River in California (De Candolle incorrectly stated the specimen had been collected in Chihuahua, Mexico, based on incorrect information provided by Engelmann). Engelmann published a more complete description in 1876, including its distribution and habit, but according to Keuter and Manos (Keuter & Manos 2019), Engelmann’s account more accurately describes Quercus kelloggii or Q. × morehus. The epithet is often misspelt wislizenii (e.g. Bean 1976), presumably on the assumption that it honours a Dr. Wislizenius rather than Wislizenus (cf. Q. sartorii named in honour of Sartorius), or even a Dr. Wislizen. But the ICN recommends that substantival epithets formed from personal names already in Latin should be given the appropriate Latin genitive form, and wislizeni for Wislizenus is included in the list of examples (Turland et al. 2025 Recommendation 60C.1).

It is likely that what Albert Kellogg described as Quercus arcoglandis is the same species. Though some references cite it as a synonym of Q. agrifolia, following Sargent (1895), the trees at the type location near Fort Tejon in southern California are what is now Q. wislizeni, according to Keuter and Manos (2019). The type specimen and illustration are presumed destroyed by the fire following the 1906 San Francisco earthquake, so it is difficult to determine the identity of Kellogg’s plant. Should it be confirmed that it is the same as Q. wislizeni, Kellogg’s name would have priority, as it was published in 1855 (Cameron 2023).

Frederick Adophus Wislizenus was born in Königsee, Thuringia, Germany, in 1810. His family was of Polish origin, and the name was derived from the town of Wiślica, in south-central Poland. The Latinized form of the surname was retained by an ancestor who in medieval or early post-Renaissance times studied at a university where all instruction was given in Latin. Wislizenus seems to have had a penchant for adventure. As a student at Jena, he participated in a failed armed revolt, which forced him to flee first to Strasbourg and then Zurich, where he completed his medical studies in 1834, pausing briefly to join a movement in unsuccessful support of Manzini’s effort to free Italy from monarchical rule. His wanderlust took him to Paris and New York, where he yielded to the attractions of the West and headed to St. Louis in 1836. In 1839 he joined a caravan of fur traders hoping to follow the Oregon Trail, but had to turn back at Fort Hall, Idaho. In 1846 he again set off, travelling through Santa Fe and Mexico, where he was made prisoner of war in Chihuahua. This is evidently the source of Engelmann’s confusion regarding the locality of Wislizenus’ specimen of Q. wislizeni. He collected that specimen while on what appears to be a final adventure: shortly after the birth of his first son, while his wife stayed with relatives in New England, he absconded from domestic duties and got as far as Panama and California, before finally returning to his family and taking them to St. Louis in 1852. For the rest of his life, he pursued scientific interests, founding with Engelmann and others the Academy of Sciences of St Louis and continuing with meteorological and botanical studies until his eyesight started to fade and he went blind. He died in 1889. He had dropped Frederick from his name before 1848 and signed himself “Dr. A. Wislizenus” (Schlueter 1938).

The common name Interior Live Oak derives from the term for an evergreen oak in the US, Live Oak, first applied to Quercus virginiana in the 1600s, with ‘Interior’ added to distinguish it from Coast Live Oak (Q. agrifolia), in reference to its inland distribution.