Evolution of the Arctostaphylos genus is relatively recent, with hybridization playing an important role; however, convergent evolution patterns appear to complicate cladistic constructions for certain portions of the genus cladogram. In any case, fossil ancestors of the Arctostaphylos genus have been suggested to have occurred in the Middle Miocene, with modern species beginning to take shape in the Late Tertiary. It has been further posited that in the earlier Tertiary a greater species diversity was present, influenced by influence of floristic influence of southwestern North America ancestors. This hypothesis also suggests that the present palette of California Arctostaphylos species became more depauperate upon arrival of a cooler drier climate in the Late Tertiary.These evolutionary views are coincident with other research that points to fire-dependent plant associations developing in the Late Miocene in California.
Present species distribution of Arctostaphylos morroensis is restricted to a very small coastal land area extent on the eastern part of Santa Cruz Island, California. This island is among the northern element of the North Channel Islands in the eastern Pacific Ocean.
Regularity: Regularly occurring
Global Range: Endemic to Santa Cruz Island, one of the northern Channel Islands off the coast of California. Occurs on the eastern part of the island (Hickman 1993). There are some reports of this species having been collected from the California mainland, but these appear to be erroneous (CNPS 2009).
Catalog Number: US 1651687
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Preparation: Pressed specimen
Collector(s): J. T. Howell
Year Collected: 1931
Locality: China Harbor., Santa Barbara, Santa Cruz Island, Santa Barbara Islands, California, United States, North America
- Isotype: Eastwood, A. 1933. Leafl. W. Bot. 1: 62.
Comments: Rocky shale substrates within chaparral and closed-cone coniferous forest communities. Co-occurring species include island scrub oak (Querus pacifica), a prostrate variety of chamise (Adenostoma fasciculatum var. prostratum), and toyon (Heteromeles arbutifolia). 100-500 m.
National NatureServe Conservation Status
Rounded National Status Rank: N3 - Vulnerable
NatureServe Conservation Status
Rounded Global Status Rank: G3 - Vulnerable
Reasons: Endemic to Santa Cruz Island, California. Can be common to dominant in certain vegetation communities on the eastern part of the island (e.g. island chapparal communities on Monterey Shale bedrock). This species exhibited a a documented increase between 1991-1992 and 1995-1996, following feral sheep removal. While the long-standing threat of damage by feral ungulates (sheep, pigs, cattle) has now abated, increases in non-native plants following ungulate removal may pose an increased threat of competition to this species.
Global Short Term Trend: Relatively stable to increase of 25%
Comments: Arctostaphylos viridissima exhibited a documented increase between 1991-1992 and 1995-1996, following feral sheep removal (Klinger et al. 2002).
Global Long Term Trend: Decline of 10-90%
Comments: Sheep, pigs, and cattle were introduced to Santa Cruz Island in the early to mid 1800s and subsequently established feral populations. These animals reached large population sizes (e.g. 50,000+ sheep in the 1890s, 800-4500 pigs in the 1990s) (Klinger et al. 2002) and had significant negative impacts on the native vegetation. Cattle were mostly removed in 1988; sheep were eradicated through efforts from 1981-2000; and pigs were removed between 2005 and 2007 (Klinger et al. 2002, Ramsey et al. 2009).
Comments: Feral ungulates (sheep, pigs, cattle) posed a threat to this species in the past; these animals have now been eradicated from Santa Cruz Island. However, increases in non-native plants following ungulate removal may pose an increased threat of competition to this species (Klinger et al. 2002).
Arctostaphylos viridissima is a species of manzanita known by the common names whitehair manzanita and McMinn's manzanita. It is endemic to Santa Cruz Island, one of the Channel Islands of California.
Arctostaphylos viridissima is a shrub varying in shape and size. It may be a matted bush one metre (~3 ft) tall to a spreading treelike form over 4 metres (~12 ft) in height. Its stem and branches are covered in peeling red bark and its smaller twigs are woolly and bear long white bristles. The leaves are oval in shape, fuzzy when new and green and shiny when mature, reaching 3.5 cm.
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