You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="Bactris_setosa_seedling_HU.jpg|5443" />
  </query-continue>
  <query>
    <pages>
      <page pageid="18" ns="0" title="Bismarckia Nobilis" />
      <page pageid="2081" ns="0" title="Beccariophoenix fenestralis" />
      <page pageid="2102" ns="0" title="Basselinia gracilis" />
      <page pageid="3380" ns="0" title="Bentinckia condapanna" />
      <page pageid="3395" ns="0" title="Basselinia pancheri" />
      <page pageid="3420" ns="0" title="Brahea calcarea" />
      <page pageid="5443" ns="0" title="Bactris setosa" />
    </pages>
  </query>
</api>