Mammillaria elongata, form 'Cristata'
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originally posted to <b><a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a></b> as <a rel="nofollow" class="external text" href="https://flickr.com/photos/28567825@N03/3104091406">'Cristata' (Mammillaria elongata)</a>