Occasionally you’ll see a tree or a fence drenched by a mound of greenery. The small round leaves are delicately suspended on twining, wire-like vines that are dark purplish-brown. This is mattress vine, or Muehlenbeckia complexa. Its other names are wire vine (because of the wiry stems?) and maidenhair vine (because the leaves are similar to those of maidenhair fern?).
Mattress vine is a native to New Zealand that occasionally can be seen growing wild here in California. It’s often grown as an ornamental for walls or topiaries, but is considered a problematic invasive in certain places–such as the Golden Gate National Recreation Area. You can see it growing in large mounds at the bunkers on Fort Cronkhite, as well as at Land’s End and the Presidio