Looks like a wild subspecies of Pleurotus.
From the article:
"Habitat: from spring to summer, rarely even in autumn, in single or bushy form. It associates, as a saprophyte, with Opuntia ficus-indica ( prickly pear ) finding ideal habitat on the trunks or cladodes (blades: parts of the stem of the prickly pear of a flattened shape which, joined together, form ramifications) dead of the plant. Findings associated with Yucca, Agave, Dracena and various Cactaceae have also been reported in the literature."
So, growing on the woody stems, it looks like. It might be worthwhile to try drying pads and inoculating them, especially very large, old, woody pads.