Cal Flora lists 83 Ceanothus species and subspecies in California. Many members of this genus are so difficult to separate from each other that I often do not even attempt to do so. Blue blossom (Ceanothus thyrsiflorus) is one that I can identify.
Blue blossom is a native shrub growing in the Coastal Ranges of Northern California and Southwest Oregon. Its habitat is canyons, slopes, wooded hills and coastal scrub below 2,000′ feet. The blue blossom growth form varies depending on habitat. In fertile canyons and along edges of forests blue blossom is almost tree-like, while on bluffs above the sea and other exposed places it is low growing, prostrate or even forms mats.
Blue blossom branches are flexible. The bark is bright red-brown and separates into scales while the twigs are green and ribbed.
The alternate, evergreen leaves are oblong to elliptical with serrated margins and short petioles (stems). The upper leaf blade is dark green and hairless. The lower surface is lighter green and slightly hairy especially along the three prominent midveins.
Blue blossom inflorescence are short, narrow, roundish or cylindrical clusters. The flowers have five deep to pale blue (or even white) petals, five sepals and five stamens with elongated filaments opposite the petals. The ovary is three lobed and has a three-cleft style.
Like all Ceanothus, blue blossom fruits are a three-lobed capsule. The capsules are sticky, round and slightly lobed at the summit. The smooth seeds are convex on one side.
Blue myrtle, blueblossom and California lilac are other colloquial names for C thyrsiflorus. The genus name comes from the Greek word “keanothus”, the name used for a spiny plant. The species name means “with flowers in a thyrse”. A thyrse is a “compact, cylindrical or ovate panicle with an indeterminate main axis and cymose sub-axes”.
Blue blossom is abundant following wildfires or logging. It is also a popular ornamental planting.
These blue blossom specimens were found along California Highway 101 between Trinidad and Patrick’s Point (Humboldt County) in May.