The only native members of Betulaceae in the Bay Area are California Hazelnut, and the Red and White Alders. Other trees from the Birch family are transplants from other parts of the continent, like the white birch so popular with expatriated midwesterners like myself.
The leaves on these plants are all alternate and deciduous, and distinctive amongst coastal trees with their pronounced crinkly vein pattern, simple ovate shape and teethed margins. At least one or both sex of the flowers are in catkins, with a woodly fruit being produced.
Betulaceae in general, and Alders in particular, have complex arrangements with bacteria and fungi for the delivery of nutrients through their root systems. Mature stands of Alders and Hazelnut in mixed forest habitats are usually a pretty good sign of good mushroom hunting areas.
Flowers: Staminate flowers in catkins, 1 inch long; Tiny pistillate flowers with 2 red stigmas each at joints of stems.
Blooms: February - April.
Leaves: Alternate, ovoid, slightly notched at base (compared with Alder leaves), fuzzy with toothed margins.
Fruit/Seeds: Nuts in woody shells enclosed in a leafy husk; about 15mm (5/8 inch) long; sometimes paired at base. June - August.
Location: Northern (partially shaded) slopes; Hazelnut trail in San Pedro Valley Park and throughout the Pacifica side of the mountain, occasional on the Montara side.
Status: Native - Common.
Further description & Comment: Woody deciduous shrub, 5 to 10 feet tall, usually in dense stands.
A unique plant community of Corylus cornuta var. californica. and Polystichum minutum. (Western Sword Fern) grows along San Pedro Mountain Road north of the Saddle Pass area on the Pacifica side. It is unique in that such a large community of these two plants has never been observed anywhere else in the world, and no one (that I've heard of) has been able to explain why this community thrives in this one place and no where else.
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