I don't believe there are any (or many) web resources available (none that I could find on a casual glance, anyway). Fortunately, computers and the Internet is not the be-all and end-all of reference information. You will probably want to seek out this book: "Agaves, Yuccas, and Related Plants" It contains keys to identifying yuccas. Gary and Mary F. Irish. Timber Press, July 2000 ISBN: 0881924423 Gary Irish is a former director of public horticulture at Desert Botanical Garden in Arizona. Google Search
