You might check the library for books on perennials to help you familiarize yourself with the leaves of common perennials. You will find pictures of many common annual and perennial flower seedlings in the book "Park's Success with Seeds," which is now out of print. Perhaps your local library can locate a copy for you. Pictures of weed seedlings may be of value to you as well. Here are some useful publications from the University of Minnesota:
Minnesota Weed Seedling Photo Collection
Annual Broadleaf Weed Seedling Identification
Annual Grass and Perennial Weed Seedling Identification
Weed Seedling Identification (discusses characteristics of grass and broadleaf weeds)
