aztec cactus coin eagle flag island lake legend Mexico Mexico City nopal sign snake zocalo agricultural pest fast-spreading food fruit glochids green fruit green. moisture introduced nopales opuntia paddle cactus platyclades prickles prickly pear prickly pear cactus fruit spikes spines textures feather ball garambulla garambulla cactus hatiora gaertneri hedgehog cereus knowlton's cactus lemaireocereus chich living rock lophophora williamsi mammillaria mammillaria plumosa mescal mezcal mistletoe cactus myrtillocactus geome night-blooming cereu opuntia cholla orchid cactus pediocactus knowlton abundance abundant agricultural-pest edible edible-prickly-pear fruiting green green-fruit Indian-fig moisture opuntia-ficus-indica paddle-cactus perennial prickly-pear prickly-pear-cactus-fruit red ripe ripe-fruit weed