a white cultivar of <a href="//commons.wikimedia.org/wiki/Ipomoea_tricolor" title="Ipomoea tricolor">Ipomoea tricolor</a>, morning glory.  The blooms are about five inches across.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/49024304@N00">anyjazz65</a> from USA
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/49024304@N00/46978264/">Moonflower</a>