Arctostaphylos densiflora, known by the common name Vine Hill manzanita, is a very rare species of manzanita. It is endemic to Sonoma County, California, where it is known from only one extant population of 20 to 30 individual plants. These last wild members of the species are on land near Sebastopol which is owned and protected by the California Native Plant Society. In addition, there are five to ten plants of this manzanita taxon growing on private property about a mile away.[2] The local habitat is mostly chaparral on sandy shale soils.
Pathogenic Risk
The entire wild population is infected with the root pathogen Phytopthera cinnamomi and subject to mortality, which could result in species extinction.[3]
Plants have been propagated through a collaborative effort by California Native Plant Society (CNPS) volunteers at the Vine Hill Preserve and the CNPS Nursery located at the Laguna de Santa Rosa Foundation near Santa Rosa, California. The purpose of the effort is to outplant to establish healthy genetically diverse plants at several locations other than the Vine Hill Preserve.[3]
Arctostaphylos densiflora is a small shrub growing in low, spreading clumps under one meter in height. Of the heath family, its shiny green leaves are oval to widely lance-shaped and less than three centimeters long.[4] It bears inflorescences of light to bright pink urn-shaped flowers. The fruit is a drupe about half a centimeter wide.
Ecological Relationships
The flowers of this species provide nectar for butterflies and native bees in the spring, berries provide food for birds in the late summer, and the low-growing habit of the plant make it a good home for California valley quail and wrentit nests. (Lowe 1999)[5]
Habitat
Roadside banks and neighboring areas in chaparral habitat with acid marine sand (York 1987).[6]
Species differentiation
A. densiflora likely appeared about 1.5 million years ago, although the Arctostaphylos genus itself arose in the Miocene era.[7]
^ abcMoore, Mark (Summer 2023). "Vine Hill Manzanitas at the Humboldt Botanical Garden". The Botanical Guardian. Eureka, California: Humboldt Botanical Garden: 6.
^Lowe, M. (1999). The Gardner's Guide to the Susal Creek Watershed: A Home Companion to Growing Native Plants. Aquatic Outreach Institute, Susal Creek Watershed Awareness Program.
^York, R. P. (1987). Elias, T. S. (ed.). California's most endangered plants. In: Conservation and management of rare and endangered plants. Sacramento, California: California Native Plant Society. pp. 109–120.
