Arctostaphylos

Distribution

The majority of Arctostaphylos species can be found within the California floristic province. However one species, A. uva-ursi (common bearberry), is adapted to arctic and subarctic climates and has a circumpolar distribution in northern North America, Asia and Europe.

An unusual association of manzanita occurs on Hood Mountain, in Sonoma County, California, where stands of pygmy forest dominated by Hesperocyparis sargentii are found.

Evolution

Arctostaphylos falls within the Arbutoideae subfamily along with Arbutus, Arctous, Comarostaphylis, Ornithostaphylos, and Xylococcus.

Arctostaphylos is the most diverse genus within this clade. The complex permutation of modern flora can be attributed to the change from the Cretaceous to the Tertiary. During the Oligocene geologic uplift and an altering climate restricted a majority of the Arbutoideae to western North America. Post Pleistocene, the growing changes in the edaphos along with climatic shifts and the incredibly unique topography within California, caused dramatic speciation, specifically within the genus Arctostaphylos.

Fossil record

One fossil fruit of †Arctostaphylos globula and several fossil fruits of †Arctostaphylos menzelii have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.

Ecology

Arctostaphylos can usually can be found on sites with poor soil. Mycorrhizal fungi are a large reason this genus can tolerate low nutrient conditions. Many of California's shrublands experience a high intensity fire regime which habitually burn completely through stands of manzanitas. Many chaparral species have developed certain adaptations to persist post fire.

One way manzanitas persist is through seed banks. Seed banks are characteristic of all species within Arctostaphylos. Manzanitas have seed that is dispersed in a dormant stage, only germinating post fire due to chemicals found in smoke. Obligate seeders lack a lignotuber/burl and are killed by fire. In contrast, facultative-seeders or burl formers resprout after fire. Most species are obligate seeders, and population survival depends on post-fire recruitment. It is known that rodent caches are crucial to the development of the seed bank.

In Arctostaphylos all species produce flowers with poricidal anthers. Poricidal anthers produce pollen that is dehisced toward the floral opening through an apical pore on the anther, often during a process call buzz pollination. In Arctostaphylos, pollination of the unique urn shaped flowers is achieved through sonication or buzz pollination . Buzz pollination is the process when certain bee species contract their indirect flight muscles on flowers extremely fast, these vibrations then release pollen from poricidal anthers and onto the bee's body.

Arctostaphylos species are used as food plants by the larvae of some Lepidoptera species including Coleophora glaucella and Coleophora arctostaphyli (which feeds exclusively on A. uva-ursi).

Cultivation

Arctostaphylos are used in the horticultural trade across much of California. Prized for being drought tolerant, low maintenance and aesthetically interesting, Arctostaphylos hybrids and cultivars are common across many gardens.

Taxonomy

Ranges

• Subgenus Micrococcus
  • Sect. Micrococcus

• Subgenus Arctostaphylos, which has three sections:
  • Sect. Arctostaphylos

• • Sect. Foliobracteata

• • Sect. Pictobracteata

• Unassigned

See also the closely related genus Comarostaphylis, previously often included in Arctostaphylos.