Adult females are reasonably large, with an abdomen about the size of a large pea. They can change color to match their background, and are often found on yellow flowers (hence the goldenrod name). The front legs are long and powerful, much like those of a crab. They are described (and photos show) a reddish color 'chevron' or V-shaped marking, but the one in my garden definitely had a black V. This marking is thought to attract bees.
So there you have it... everything you ever wanted to know (and probably more!) about the Goldenrod Crab Spider.