Quercus parvula

Quercus parvula, the Santa Cruz Island oak, is an evergreen red oak (Series Agrifoliae, Section Lobatae) found on north-facing Santa Cruz Island slopes and in the California Coast Ranges from Santa Barbara County north to Mendocino County. It was taxonomically combined with Quercus wislizeni until resurrected as a separate species by Kevin Nixon in 1980.[2] The type locality of Q. parvula var. shrevei (originally described by C.H. Muller as Q. shrevei) is Palo Colorado Canyon in Monterey County.

Quercus parvula
Quercus parvula

Near Threatened  (IUCN 3.1)[1]
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Fagales
Family: Fagaceae
Genus: Quercus
Subgenus: Quercus subg. Quercus
Section: Quercus sect. Lobatae
Species:
Q. parvula
Binomial name
Quercus parvula
Greene

Three varieties of Q. parvula are currently recognized:[3]

  • Q. parvula var. parvula,[4] Santa Cruz Island oak[3] - Santa Cruz Island, California. Recent work suggests Q. parvula var. parvula to be Q. parvula var. shrevei x Q. wislizeni.
  • Q. parvula var. shrevei,[2][5] Shreve oak[3] or forest oak[6] - central and northern coastal California. If further studies support the recently identified issues with var. parvula, this taxon may be revised to Q. shrevei.
  • Q. parvula var. tamalpaisensis, Tamalpais oak[7] - Marin County, California. This is an invalid taxon. Recent DNA studies have shown Tamalpais oak to be a hybrid between Q. wislizeni and Q. parvula var. shrevei.[8]

Q. parvula differs morphologically from its close relative Q. wislizeni in the following ways:[8]

  • Leaf blades are larger, > (2)4 cm long rather than < 4(6) cm
  • Leaf blades are thinner, generally < 0.26 mm near the apex rather than usually > 0.26 mm
  • Current year twigs are 5-sided rather than ± roundish in cross section
  • Leaf petioles and current year twigs are glabrous to sparsely hairy rather than moderately to very hairy
  • Nut tips are blunt rather than more sharply pointed
  • Abaxial golden glandular uniseriate leaf blade trichomes are missing or sparse rather than moderate to dense
  • Abaxial multiradiate leaf blade trichomes are missing or sparse on the midvein rather than occasional to common
  • Secondary leaf blade veins are raised abaxially rather than ± not raised

Q. parvula and Q. wislizeni never produce newly emerging leaves with a velvety coating of red bulbous trichomes on the abaxial (upper) surface. This separates them from Q. kelloggii and both varieties of Q. agrifolia which produce such leaves.

Ecology

Mainland Q. parvula is commonly found with or near Sequoia sempervirens (coast redwood), and often near Quercus agrifolia var. agrifolia (coast live oak) and Notholithocarpus densiflorus (tanoak).

Q. parvula differs ecologically from Q. wislizeni in the following ways:[8]

  • Island or coastal habitat rather than Sierra foothills
  • Associates with Sequoia sempervirens rather than Pinus sabiniana

Hybridization

Quercus parvula is theoretically capable of hybridizing with all of the other California red oaks except the higher elevation southern California Quercus agrifolia var. oxyadenia[9] (sharpacorn oak[10]) from which it is separated by the Transverse Ranges. However Q. parvula's generally later flowering time (April–May versus February–April for Q. kelloggii, Q.wislizeni and Q. agrifolia) may limit genetic exchange with other Lobatae.

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References
  1. "Quercus parvula". IUCN Red List of Threatened Species. 2016. 2016. Retrieved 4 November 2017. data
  2. K. Nixon, "A Systematic Study of Quercus parvula Greene on Santa Cruz Island and Mainland California," Master's Thesis, 1980.
  3. Jepson Flora Project (eds.) 2015 Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html July 17, 2015
  4. Greene, Pittonia 1:40 (1887)
  5. K. Nixon, C.H. Muller, “New Names in California Oaks,” Novon 4(4):391 (1994)
  6. R. Morgan et al, in Santa Cruz Cnty. Pl. Checklst., 22 (2005)
  7. S.K. Langer, “A New Oak On Mount Tamalpais,” Four Seasons, 9(3): 21-30 (1993)
  8. Duncan A. Hauser, Al Keuter, John D. McVay, Andrew L. Hipp and Paul S. Manos, The evolution and diversification of the red oaks of the California Floristic Province (Quercus section Lobatae, series Agrifoliae), October 2017 104:1581-1595
  9. Torr., Sitgr. Rep., 172, pl. 17 (1853)
  10. J.G. Cooper, Smithsonian Rep. 1858: 261 (1859)
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