Onion
<p >The <b>onion</b> (<i>Allium cepa</i>), which is also known as the <b>bulb onion</b>,<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-0" >[1]</a></sup> <b>common onion</b><sup id="cite_ref-Rabinowitch_and_Currah_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-Rabinowitch_and_Currah-1" >[2]</a></sup> and <b>garden onion</b>,<sup class="Template-Fact" >[<i><a href="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed" >citation needed</a></i>]</sup> is the most widely cultivated species of the genus <i><a href="http://en.wikipedia.org/wiki/Allium" title="Allium" >Allium</a>.</i><sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-2" >[3]</a></sup> The genus <i>Allium</i> also contains a number of other species variously referred to as onions and cultivated for food, such as the <a href="http://en.wikipedia.org/wiki/Japanese_bunching_onion" title="Japanese bunching onion" class="mw-redirect" >Japanese bunching onion</a> (<i>A. fistulosum</i>), <a href="http://en.wikipedia.org/wiki/Egyptian_onion" title="Egyptian onion" class="mw-redirect" >Egyptian onion</a> (<i>A.</i> ×<i>proliferum</i>), and <a href="http://en.wikipedia.org/wiki/Canada_onion" title="Canada onion" class="mw-redirect" >Canada onion</a> (<i>A. canadense</i>).<sup id="cite_ref-Rabinowitch_and_Currah_1-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-Rabinowitch_and_Currah-1" >[2]</a></sup> The name "<a href="http://en.wikipedia.org/wiki/Wild_onion" title="Wild onion" >wild onion</a>" is applied to a number of <i>Allium</i> species. Onion is most frequently a <a href="http://en.wikipedia.org/wiki/Biennial_plant" title="Biennial plant" >biennial</a>, although it can also be a triennial or a <a href="http://en.wikipedia.org/wiki/Perennial" title="Perennial" class="mw-redirect" >perennial</a>.
The vast majority of cultivars of <i>A. cepa</i> belong to the "common onion group" (<i>A. cepa</i> var. <i>cepa</i>) and are usually referred to simply as "onions". The Aggregatum Group of cultivars (<i>A. cepa</i> var. <i>aggregatum</i>) includes both <a href="http://en.wikipedia.org/wiki/Shallots" title="Shallots" class="mw-redirect" >shallots</a> and <a href="http://en.wikipedia.org/wiki/Potato_onion" title="Potato onion" >potato onions</a>.<sup id="cite_ref-Rabinowitch_20-21_3-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-Rabinowitch_20-21-3" >[4]</a></sup>
<i>Allium cepa</i> is known exclusively in cultivation,<sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-4" >[5]</a></sup> but related wild species occur in Central Asia. The most closely related species include <i>Allium vavilovii</i> (Popov & Vved.) and <i>Allium asarense</i> (R.M. Fritsch & Matin) from <a href="http://en.wikipedia.org/wiki/Iran" title="Iran" >Iran</a>.<sup id="cite_ref-prota_5-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-prota-5" >[6]</a></sup> However, Zohary and Hopf warn that "there are doubts whether the <i>A. vavilovii</i> collections tested represent genuine wild material or only feral derivatives of the crop."<sup id="cite_ref-6" class="reference" ><a href="http://en.wikipedia.org/wiki/Onion#cite_note-6" >[7]</a></sup></p>