NOOOO, Stop, Don't pull this weed!  Your butterfly caterpillars will prune it for you if you just let it grow a bit, and you'll get to enjoy watching them in your yard.  The leaves are Passiflora suberosa, commonly known as Corky Stem Passion Flower or 'that weedy vine on the fence'.  Note the wide variation in leaf shape to the sides, and on the seedling below.

I've put passion vines all over my yard because three different kinds of large beautiful butterflies lay eggs on them here in South Florida.  Planting the right passion vine is one of the easiest ways to make your yard a butterfly habitat if these butterflies are native to your area:
    Zebra Heliconian
    Gulf Fritillary
    Julia Dryas
Now that my plants have had some time to grow without a hurricane ripping them all up, I have LOTS of butterflies in my yard.

The photos above are all Passiflora Suberosa, Corky Stem Passionvine. The purple one on the right might be Passiflora incarnata; it's similar.

Whether it is or not, the caterpillars eat it up. Stay away from the red flowered Passiflora vines because the butterflies might lay eggs on them but the caterpillars can die. It depends on which red flowered vine it is, but I avoid them all because I don't know.  Look up which Passiflora are native to your area and check your local butterfly information to see what lives on it.

To make sure you get the right passion vine for your area, contact a local expert or look them up carefully. I've learned a lot from the folks at both of the plant places below, and purchased plants from them.  The very best is getting a plant you don't have, and buying it with caterpillars all ready chewing it up! What a bonus! Meadow Beauty answered one of my 'which plant is best' questions with, "Follow the butterflies." So I did, and just before I bought their plant, I got to watch a butterfly lay eggs on it. It was fabulous, and those critters emerged in MY yard!

Palm Beach - Meadow Beauty Nursery

Broward - The Garden Gate