Arctostaphylos

Arctostaphylos (/ˌɑːrktoʊˈstæfɪləs, -lɒs/; from ἄρκτος árktos "bear" and σταφυλή staphulḗ "bunch of grapes")^[1][2] is a genus of plants within the family Ericaceae.^[2] Many plants within the genus Arctostaphylos are also commonly called manzanitas(/ˌmænzəˈniːtəz/) or bearberries.^[3] There are 107 taxa within Arctostaphylos, 106 of which are found in the California Floristic Province.^[4] From prostrate shrubs to small erect trees, Arctostaphylos is known for characteristic red bark, urn-shaped flowers and being fire adapted .^[2]

Stem - Usually red-stemmed, Arctostaphylos can range from completely smooth to grey-shreddy bark.  In some species, stems can be found with tomentum, or hairs.^[2]

Burls or lignotubers are an enlarged stem base or root crown carrying dormant buds for resprouting post disturbance.^[5] About ⅓ of all species are Burl formers.^[4] Burls can be used to help identify down to the species level.^[2]

Leaves - Tending to grow alternately, all Arctostaphylos species are evergreen.^[2] A common step to help better identify down to the species level is by examining leaf surfaces.^[2]

For example, Arctostaphylos tomentosa has stomata only abaxially, while Arctostaphylos glandulosa subsp. glandulosa is bifacial, having similar surfaces on the top and bottom sides of the leaf.^[2]

Flowers - A characteristic feature of Arctostaphylos is its urn-like flowers.^[2] The corolla is usually composed of 5 fused petals.^[2] These flowers are very common in the clade Arbutoideae.^[6]

Fruit - Classified as a drupe,^[2] Arctostaphylos fruit is commonly spheric.^[2] The seeds found within the mealy mesocarp are often called stones.^[2]

The majority of Arctostaphylos species can be found within the California floristic province.^[4] One species, however, A. uva-ursi (common bearberry), is adapted to arctic and subarctic climates and has a circumpolar distribution in northern North America, Asia and Europe.^[6]

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

Arctostaphylos falls within the Arbutoideae subfamily along with Arbutus, Arctous, Comarostaphylis, Ornithostaphylos, and Xylococcus.^[6]

Arctostaphylos is the most diverse genus within this clade.^[4] The complex permutation of modern flora can be attributed to the change from the Cretaceous to the Tertiary.^[7] During the Oligocene geologic uplift and an altering climate restricted a majority of the group arbutoideae to western North America.^[7] 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.^[6]

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.^[8]

Arctostaphylos can usually can be found on sites with poor soil. Mycorrhizal fungi are a large reason this genus can tolerate low nutrient conditions.^[4] Many of California's shrublands experience a high intensity fire regime which habitually burn completely through stands of Manzanitas.^[4] Many chaparral species have developed certain adaptations to persist post fire.^[4]

One way manzanitas persist is through seed banks. Seed banks are characteristic of all species within Arctostaphylos.^[9] Manzanitas have seed that is dispersed in a dormant stage, only germinating post fire due to chemicals found in smoke.^[4] Obligate seeders lack a lignotuber/burl and are killed by fire. In contrast, Facultative-seeders or Burl formers resprout after fire.^[10] Most species are obligate seeders, and population survival depends on post-fire recruitment.^[9] It is known that rodent caches are crucial to the development of the seed bank.^[9]

In Arctostaphylos all species produce flowers with poricidal anthers. ^[11][2]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.^[11][12]In Arctostaphylos, pollination of the unique urn shaped flowers is achieved through sonication or buzz pollination ^[11]. 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^[12].

Arctostaphylos species are used as food plants by the larvae of some Lepidoptera species including Coleophora arctostaphyli (which feeds exclusively on A.uva-ursi) and Coleophora glaucella.^[13]

Arctostaphylos are used in the horticultural trade across much of california. ^[14] Prized for being drought tolerant, low maintenance and aesthetically interesting, Arctostaphylos hybrids and cultivars are common across many gardens.^[14]

• 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.

• Hickman, James C. (1993), The Jepson Manual: higher plants of California, Berkeley and Los Angeles, California: University of California Press, ISBN 0-520-082559
• Hogan, C. Michael (2012), "Arctostaphylos", in McGinley, M.; C. J. Cleveland (eds.), Encyclopedia of Earth, National Council for Science and the Environment
• Kauffmann, Michael; Parker, Tom; Vasey, Michael; Bisbee, Jeff (2021-07-29), Field Guide to Manzanitas: California, North America, and Mexico (2nd ed.), Backcountry Press, ISBN 978-1941624159
• Treatment from the Jepson Manual
• Wells, Philip V. (2000), Manzanitas of California, Lawrence, Kansas: University of Kansas, Department of Ecology & Evolutionary Biology, ISBN 0-933994-22-2
• Wells, Philip V. (1992). "Subgenera and sections of Arctostaphylos". The Four Seasons. 9: 64–69.

• Jepson Manual Treatment