Some species have a milky sap that can be toxic. The fibrous stems of A. cannabinum. were used by Native Americans for making ropes and cords. Neither species has been found on Montara Mountain at this time. Glossy, dark green, ovoid. Most trails and creek at lower elevations - prefers shaded areas.
Eradication is difficult, as Periwinkle flowers and seeds continuously all year long.
Some success has been reported with tarping clumps of it with black plastic for 6 to 12 months. Effective, but not awfully attractive in a park. For the most part, we just keep yanking it out as we find it. Apparently a powerful temporary treatment for acute short-term need, but dangerous if used regularly.