Santa Rosa Island
With an area of 84 square miles, Santa Rosa Island is the second-largest of the Northern Channel Islands and is also the second-largest island in the entire chain. It is situated 26 miles south of the Santa Barbara coastline. San Miguel Island, Santa Rosa’s closest island neighbor, is located 3 miles to the west.
The flora of Santa Rosa Island includes about 400 native taxa and 100 non-native taxa. The natural distribution of at least 38 of the island’s native taxa are restricted to two or more of the California Islands; 5 plant taxa have been found only on Santa Rosa Island.
The five plant taxa which have been found only on Santa Rosa Island are:
- Arctostaphylos confertiflora (Santa Rosa Island manzanita)
- Dudleya blochmaniae subsp. insularis (Santa Rosa Island live-forever)
- Dudleya gnoma (East Point dwarf dudleya)
- Gilia tenuiflora subsp. hoffmannii (Hoffmann’s slender-flowered gilia)
- Pinus torreyana subsp. insularis (Santa Rosa Island Torrey pine)
One additional plant species (Castilleja mollis) is now known only from Santa Rosa Island but previously occurred on San Miguel Island as well.
Gilia tenuiflora subsp. hoffmannii
Common Names: Hoffmann's gilia, Hoffmann's slender flowered gilia, Hoffmann's slender flowered gilia, Slender flowered Gilia
Family: Polemoniaceae (Phlox Family)
Notes: Included in the CNPS Inventory of Rare and Endangered Plants on list 1B.1 (rare, threatened, or endangered in CA and elsewhere)
At least one insular endemic is now presumed to be extinct on the island:
- Berberis pinnata subsp. insularis (island barberry) - previously known from Santa Rosa (last seen there in 1930) and West Anacapa (last seen there in the 1980s). This taxon is now known only from a few small colonies on the west end of Santa Cruz Island.
On the other hand, two important insular endemics were found on Santa Rosa Island as recently as 1996:
- Arabis hoffmannii (Hoffmann’s rock cress) - thought to be extinct on Santa Rosa Island but rediscovered in LoboCanyon. It is also known from a few populations on Santa Cruz Island.
- Malacothrix indecora (Santa Cruz Island malacothrix) - an insular endemic which was previously known only from San Miguel and Santa Cruz Islands, was found just west of the mouth of Lobo Canyon.