Quercus parvula Greene

Shrub 1–3 m (var. parvula) or tree to 17 m (var. shrevei, q.v.). Bark grey, smooth or weakly fissured. Branchlets pubescent at first, then glabrous, greenish-brown, ribbed. Leaves evergreen, leathery, 3–14 cm long, oblong, lanceolate or ovate to obovate, upper surface olive-green to dark green and glabrous, lower surface dull olive-green and glabrous, six to eight secondary veins, not prominent, on each side of the midrib, which is prominent beneath, margin generally entire, rarely dentate, apex acute to acuminate; petiole 0.2–1 cm long. Cupule bowl-shaped, 1.2–1.5 × 0.6–1 cm, tomentose inside; scales flat (not tubercled), rather thin, brown, obtuse, covered with minute hairs. Acorn barrel-shaped to ovoid with an abruptly tapered apex, 3–4.5 cm long. Flowering in late spring, fruiting the year after flowering (USA). (Tucker 1993; Greene 1887; le Hardÿ de Beaulieu & Lamant 2010).

Distribution  United States California (Santa Barbara County, Santa Cruz Island, eastern Transverse Ranges)

Habitat Woodland and chaparral in canyons and on slopes below 500 m.

USDA Hardiness Zone 8

RHS Hardiness Rating H4

Conservation status Near threatened (NT)

Taxonomic note This species is often confused with Quercus wislizeni, starting with the author who first described it in 1887, E.L. Greene. Just two years following his publication of Q. parvula, he decided he had been hasty in treating it as a new species. Though its maritime habitat, small size, and the different pubescence on the cups seemed to justify distinguishing it from Q. wislizeni, Greene was later informed of mainland specimens on Mount Tamaulipas (northern California) of what he understood to be Q. wislizeni, and that were very similar to the oak he described (Greene 1889). Quercus parvula was treated as a synonym of Q. wislizeni by Jensen (1997) (as Q. wislizenii). Kevin Nixon, in his Master’s thesis (1980), studied the taxon and resurrected Greene’s Q. parvula, including in its circumscription the shrubby oaks described by Greene, found on Santa Cruz Island and on the nearby mainland, and also the coastal trees that Muller had described as Q. shrevei in 1938, a name Nixon recombined as Q. parvula var. shrevei. Q. parvula can be distinguished from Q. wislizeni by its larger leaves (3–14 cm vs. 2–5 cm long), distinctive leaf undersides (dull olive-green vs. shiny yellow-green) and acorns (abruptly tapered vs. gradually tapered); var. parvula is a shrub to 3 m, while var. shrevei makes a tree to 17 m. Q. parvula is more typical of wetter areas in the coastal fog belt; in contrast, Q. wislizeni is typical of arid slopes in the interior. Hybrids of the two species occur naturally in the San Francisco Bay Area, perhaps also involving Q. agrifolia, and it is these problematic populations that apparently led Jensen to synonymise Q. parvula. The characters that distinguish the species do not change when they are grown together outside their native habitats (Keuter & Manos 2019; Nixon 2002). In 1993, Stephen K. Langer described Q. parvula var. tamalpaisensis from a small number of trees on or near Mt. Tamalpais, but this was later determined to be part of a hybrid swarm between Q. parvula and Q. wislizeni (Hauser et al. 2017). A phylogenetic study by Dodd and Papper (2019) supported the recognition of Q. parvula as a distinct species, though support of two varieties (var. parvula and var. shrevei) was less conclusive.