Calistoga Ceanothus

Ceanothus divergens is an erect mound-type shrub maturing at a height of one half to 1.5 meters. Its occurrence is restricted to a limited portion of the North Coast Ranges within only Sonoma and Napa County, California, particularly the Sonoma Mountains and the Mayacamas Mountains at elevations ranging from 150 to 950 meters. Occurrences are chiefly on volcanic slopes in chaparral or open canopy areas of mixed oak woodlands. The reddish brown plant stems are ascending to generally erect; opposite leaves are five to twelve millimeters in length, normally exceeding the width by a factor of two. There are three to eleven spiny teeth per leaf. The blue to purple flowers are exhibited in mid-February to mid-April. This species is classified as rare and of limited distribution by the California Native Plant Society, who has conducted original species field surveys for the Annadel State Park populations as recently as March, 2012; chief threats are population loss by stochasticity and aggressive brush clearing by Pacific Gas and Electric in power line corridors. The entire genus is situated in a monphyletic clade or sub-family known as the Arbutoideae, which is populated by taxa having bright fleshy berries with fibrous or bony endocarp.. Evolution of the 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.

Ceanothus divergens, commonly known as Calistoga ceanothus, is an evergreen shrub in the family Rhamnaceae, an endemic of California.