On a farm fence line, wiry brown stems intertwining to make a tangled mass - a New Zealand coastal plant - Muehlenbeckia complexa.
Pohuehue is the Maori name but it is also called wire vine, for obvious reasons. A vigorous vine, with support it can climb to 4 or 5 metres, or it will clump along the ground to form a dense groundcover - great as a shelter and nesting site for birds and a habitat for insects, lizards and other small beasties, and useful for dune reclamation or smothering introduced weeds.
But these qualities also mean that it can become a weed in its own right - it has become established and problematic in Australia and in California.
Here it is beginning to form a hedge at the edge of a paddock.
Although it looks rather dull from a distance, it has very pretty little cream coloured starry flowers and it produces black seeds held in little fleshy white cup-like berries - food for the creatures that shelter in its dense cover.
So - in the right place a really useful plant supporting the ecosystem, but an invasive pest requiring a sustained eradication/control programme in San Francisco. Success in the plant world is not always welcome in the human scheme of things.