Quercus kelloggii Newb.

Despite its common name, California Black Oak is known in cultivation and the wild for its vibrant displays of seasonal colour: young leaves emerge in spring in pinkish hues from pale salmon to fuchsia – their margins fringed with delicate elongated lobe tips – among pendant gold-green catkins; summer foliage is a lustrous deep green; chestnut-brown acorns ripen in autumn against a backdrop of yellow and russet leaves (Pavlik et al. 1991). The fissured platelets of dark grey bark, moistened by snowmelt in winter, seem to be behind the common name, though it may have come about by its resemblance to Q. velutina from the eastern US, which is known as Black Oak. It is reliably hardy in cultivation, especially in the case of high-elevation selections (Sternberg 2004).

Quercus kelloggii is widely distributed from central Oregon to the Laguna Mountains in southern San Diego County, in mountainous areas away from the immediate coast. An isolated population was found in the Sierra Pedro Mártir of northern Baja California around 1990 (Pavlik et al. 1991). It excels all other California oaks in volume, distribution, and altitudinal range. It has an extensive north-south range of over 1200 km, extending from just north of Eugene, Oregon, and running southward through the Klamath, Cascade, and North Coast ranges as well as most of the Sierra Nevada (McDonald 1969). It grows in an upland climate with hot, dry summers and moist, cold winters, typically receiving more than 650 mm in precipitation (Pavlik et al. 1991).

Unlike other Californian oaks, Quercus kelloggii occurs as an affiliate to conifers and other broadleaf trees in diverse mountain communities rather than as a dominant species. It is most common in Pinus ponderosa and mixed-conifer forests, where it associates with Abies concolor and Calocedrus decurrens. In the Klamath-Siskiyou region of southwestern Oregon and northwestern California, it is a common associate in dry-site Pseudotsuga menziesii forests. In mixed-oak woodlands on the North Coast Ranges of northern California, Q. kelloggii grows in association with Q. agrifolia, Q. lobata, and/or Lithocarpus densiflorus. In low-elevation canyons throughout much of its range, California Black Oak co-dominates with Q. chrysolepis, which is usually dominant on dry sites, while Q. kelloggii is more dominant on mesic sites (Fryer 2007).

The species has no strict soil preference but is most common on dry, well-drained soil. According to McDonald (1969), internal drainage is an important factor limiting its occurrence, and the species is not found ‘with its feet wet’. It grows best on deep, slightly acidic, sandy or gravelly clay loams derived from sandstone, metavolcanic or granitic rock. It is found on thin soils and rocky slopes, but in fewer numbers and poorer form. It is rarely found on sites with clay topsoils, particularly where the clay is heavy or sticky.

The species was discovered in 1846 in Northern California. Though Elwes and Henry (1913) credit Karl Hartweg for its discovery, it is likely that John C. Frémont collected it first. Hartweg’s specimen (K000832289) can be dated to around mid-September that year, while Frémont’s (NY00253624) is dated 8 April 1846. It was introduced to cultivation in the UK a few decades later. Elwes and Henry (1913) claim it was introduced by the Earl of Ducie, who planted two trees at Tortworth, Gloucestershire, raised from acorns obtained from San Francisco in 1878. McDonald (1969) reports that it was introduced to cultivation outside the US ‘by an English earl who visited California,’ but it seems unlikely that the Earl of Ducie travelled there. They mention a smaller specimen at Kew, which fruited in 1907. Bean (1915) confirms a planting date of 1879 for the trees at Tortworth and also mentions a small tree at Kew. However, the accession number of Kew’s tree has 1873 as the year, which would make it the first introduction to Britain, a date also cited by le Hardÿ de Beaulieu & Lamant​​​​ (2010) and The Hillier Manual (Edwards & Marshall 2019). The seed was received from C.S. Sargent of the Arnold Arboretum, suggesting that the species may have been cultivated there at around the same time. However, the earliest record of Q. kelloggii in the Arnold’s database is of a plant received from Kew in 1906 (Arnold Arboretum 2025).

Though rare in cultivation during most of the past century, Quercus kelloggii is now not uncommon in specialist gardens, and no self-respecting oak collection in a temperate climate is without it. The Tree Register lists as the UK champion a tree at Eastnor Castle in Herefordshire, England, measuring 25.7 m × 106 cm dbh in 2023, but the tree was previously recorded as Q. velutina, and based on its reported characteristics, it may well be that (The Tree Register 2025). (This possible misidentification would echo that of its earliest discoverers, see below). A tree at Tortworth, from the 1879 planting, measured 21.0 m × 100 cm in 2005, but had died by 2015. The largest living Q. kelloggii specimens in Great Britain would be at Borde Hill, West Sussex (22.5 m × 80 cm in 2025) and Thorp Perrow Arboretum, North Yorkshire (24 m × 72 cm in 2022). The tree at Kew, the oldest in cultivation, measured 21 m × 65 cm in 2025, and though of fine structure, has not had space to develop a broad canopy. In Europe, a spindly specimen at Zuiderpark in The Hague, the Netherlands, measured 23.8 m × 58 cm (Monumental Trees 2025). Q. kelloggii is notable for being one of rather few Section Lobatae oaks that can still grow into a respectable tree in the cool-summer climate of northern Britain, though likely only when northern (Oregon) provenance is selected (T. Christian, pers. comm. 2026).

A suspected hybrid of Quercus kelloggii with Q. parvula var. shrevei was collected by Béatrice Chassé from Tamalpais State Park, California. Planted at Arboretum des Pouyouleix, France in 2006 it started producing acorns in 2023. Seedlings from this tree have been raised, some of which are close to Q. kelloggii while others resemble Q. parvula var. shrevei.

In New Zealand, a squat tree boasts a trunk diameter of 85 cm, reaching an estimated 15 m in height (pers. obs. RC 2019). Accessioned in 1968, it was grown from seed obtained from nearby Eastwoodhill Arboretum. If this seed came from a tree there, the parent has not survived: current accessions were planted in 2004, obtained from Appletons Tree Nursery, the largest about 10 m tall (M. Kluiters, pers. comm. 2025). Quercus kelloggii was one of seven species of section Lobatae oaks being trialled in large quantities by the Oak Action Group of Farm Forestry New Zealand in 2019 (Hurr 2019). While it is not common in Australia, especially compared with other Californian oaks, some mature specimens can be found in public collections. A tree accessioned in 1954 grows at Waite Arboretum, South Australia, but has done so very slowly, only reaching about 6 m tall, much less than other Californian oaks planted in the same year. It has a broad, ground-sweeping canopy of about 10 m in diameter. Other specimens grow at Golden Valley Tree Park, Western Australia (c. 10 m tall) and at Dunkeld Arboretum, Victoria (c. 5 m ) (B. & K. Cerlienco, pers. comms. 2025).

In habitat, California Black Oak is especially susceptible to fungi, particularly Polyporus dryophilus and P. sulphurens, which cause heart rot in the bole and larger limbs; Armillaria mellea causes decay of the roots and butt of older trees, though younger trees do not seem to be affected by it (McDonald 1969). More recently, starting in the late 1990s, it has been prone to Sudden Oak Death, a disease associated with the pathogen Phytophthora ramorum. Together with Q. agrifolia (Coast Live Oak) and Lithocarpus densiflorus (Tan Oak), it is one of the three tree species most susceptible to mortality from the disease (Barrett et al. 2006).

Native American people have traditionally favoured Quercus kelloggii acorns as a food source. They were considered to be the best-tasting acorns by California tribes, including Shasta, Mikow, and Luiseño. They stored well due to their high tannin content, and mush made from them thickened readily. The wood of young branches was used for making household implements and stout logs as support columns for ceremonial round houses. Dyes were also made from the bark (Pavlik et al. 1991).

When first seen in the wild, it was thought to be a form of section Lobatae species from Eastern North America, as it resembles them in their lobed, aristate leaves. Bentham studied the specimen collected by Hartweg in 1846 and suspected it may be a different species, which he labelled Q. sonomensis, after the place where it had been found (Sonoma). However, Liebmann had examined a specimen collected by Frémont (K000832288), also in 1846, and had determined it to be Q. rubra. Bentham noted that Frémont and Hartweg’s specimens were the same, and he was influenced by Liebmann, using his determination when publishing an account of Hartweg’s specimen in Plantas Hartwegianas in 1857 (Bentham 1839–1857). Meanwhile, Torrey had studied specimens collected by Bigelow and others, including Frémont, and thought it was a variety of what is now Q. velutina, publishing the name Q. tinctoria var. californica. Torrey also had misgivings about its identity and wrote, ‘We have not been able to point out characters sufficient to distinguish it specifically from Q. tinctoria of the Atlantic states, and it is probably a distinct species’ (Torrey 1857). Newberry shortly afterwards did find reason sufficient to distinguish it as a species, which he named in honour of his ‘friend Dr. A. Kellogg, of San Francisco, who is devoting himself with so much industry and success to the study of the plants of his adopted State’ (Newberry 1857). Kellogg was the first resident California botanist and first Curator of Botany of the California Academy of Sciences, of which he was a founding member. The following year, J.G. Cooper elevated Torrey’s var. californica as Q. californica, but this was illegitimate as he cited the earlier Q. kelloggii as a synonym (Cooper 1859). Bentham’s name Q. sonomensis, arguably the earliest name given to the species when he wrote it on a label on Hartweg’s specimen, was not published till 1864 by De Candolle, who was apparently not aware that Q. kelloggii had already been published (De Candolle 1864). Of these names, Q. sonomensis was the only one associated with a holotype or lectotype, and Q. kelloggii was not typified till 2022, when Bartholomew and Almeda designated as lectotype a specimen collected by Bigelow (NY01470684) and referred to, among others, by Torrey when describing Q. tinctoria var. californica (Bartholomew & Almeda 2022).