Heteromeles arbutifolia (; more commonly by Californian botanists), commonly known as toyon, is a common perennial shrub native to extreme southwest Oregon, California, and the Baja California Peninsula. It is the sole species in the genus Heteromeles. Toyon is a prominent component of the coastal sage scrub plant community, and is a part of drought-adapted chaparral and mixed oak woodland habitats. It is also known by the common names Christmas berry and California holly. Description Toyon typically grows from 2–5 m (rarely up to 10 m in shaded conditions) and has a rounded to irregular top. Its leaves are evergreen, alternate, sharply toothed, have short petioles, and are 5–10 cm in length and 2–4 cm wide. In the early summer it produces small white flowers 6–10 mm diameter in dense terminal corymbs. Flowering peaks in June. The five petals are rounded. The fruit is a small pome, 5–10 mm across, bright red and berry-like, produced in large quantities, maturing in the fall and persisting well into the winter. Phytochemistry The plant has been used as a treatment for Alzheimer's by indigenous people of California and recent research has found a number of active compounds that are potentially beneficial to Alzheimer's treatment. These include icaricide compounds, which protect the blood-brain barrier and prevent infiltration of inflammatory cells into the brain. Taxonomy The genera Photinia, Aronia, Pourthiaea, and Stranvaesia have historically been variously combined by different taxonomists. The genus Heteromeles as originally published by Max Joseph Roemer was monospecific, including Photinia arbutifolia Lindl. (1820), as H. arbutifolia (Lindl.) M. Roem, but the name was illegitimate (superfluous) because it included the type of the genus Photinia. This has since been corrected by conservation, and the name is therefore often written as Heteromeles M. Roem. nom. cons. (1847). Varieties Heteromeles arbutifolia var. arbutifolia (Lindl.) M.Roem. – Autonym Heteromeles arbutifolia var. cerina (Jeps.) A.E.Murray – Representative of the yellow fruiting specimens of the plant. Sporadic in distribution, and not accepted by most taxonomical authorities. Heteromeles arbutifolia var. macrocarpa (Munz) Munz (Island Christmas berry or island toyon) – A very rare insular variety limited to the Channel Islands of San Clemente and Santa Catalina and the Mexican Pacific island of Guadalupe. Characterized by shorter, broader, significantly larger leaves with revolute margins and little teeth, and floriferous inflorescences with larger fruits (8 to 10 mm). It is more susceptible to fungal infections of Spilocaea than the common