Whitethorn (Ceanothus cordulatus) is an evergreen member of the buckthorn family. With its greyish branches that look almost white at a distance and small, evergreen leaves this native shrub adds color to the winter landscape. Recently, while walking along the Pacific Crest Trail in Shasta County CA, I noticed the remains of whitethorn seed capsules clinging to the plants. The tiny capsule remnants were very delicate and fell to the ground with the least disturbance. I thought these little, almost inconspicuous cups on long stems were fascinating.
The fruit of the whitethorn is a three-chambered, triangular capsule. Each chamber or valve contains a single seed. When mature, the capsule explodes and forcibly ejects the seeds. On hot late summer and fall afternoons the “pop” of opening capsules is audible.The remaining capsule base has three ridged indentations that resemble a “peace sign”.
Whitethorn seed dispersal is autochoric (the plant has its own built-in mechanism for propelling the seeds), however most seeds fall close to the mother plant and remain there unless carried off by birds or small mammals. The seeds can remain in the duff under the parent plant for years until a fire stimulates germination.
In addition to the pictures of the whitethorn seed capsule remnants I have included photos of unopened three-chambered seed capsules.
More information on whitethorn can be found in my previous post “Whitethorn“.