Like many inventions, new cultivars of plants can be patented. For more information on plant patents, visit the U.S. Patent and Trademark Office Plant Patent website.
If a cultivar is patented, you may not propagate the cultivar without permission of the patent holder. Plant patents last for 20 years from the date of filing the patent, after that time the patent is expired and propagation is allowable. Most of the muscadine vines listed on this website that are patented originated with Ison's Nursery. The patent on some of these cultivars has expired, and others are still in force. Check the date of the patent as the pages are not updated very often. Cultivars with a patent are usually only available via Ison's Nursery, while unpatented cultivars may be available at several nurseries.