Q.Identify a Weed
It’s a vining weed with no flowers and a long, round stem (up to 12 inches or more) between two opposing leaves, which are shaped like long, thin arrows. It smells like onions when touched. Tendrils will attach to fence, other plants, etc. The vines can be several feet long. My yard is in Tucson, AZ.
That sounds like some of the weed we get here in Colorado called Bind Weed as it climbs and wraps itself around other plants and shrubs. It will bind them all up too if left too long and can kill other flowering and desirable plants. Can be very hard to get rid of even using Round Up.