This plant grew next to an Opuntia on the island of Gran Canaria (Canary Islands, Spain). It has fruits and although its stems are very strange, they are similar to those of some genera of the cactus family. There are monstrous forms of other Opuntia species, such as Opuntia monacantha. And it could be one of these forms of some of the Opuntias that grow on the islands.
Recent literature identified in Canarias feral specimens of Opuntia basilaris, O. dillenii, O. eliator, O. engelmannii, O ficus-indica, O. leucotricha, O. lindheimeri, O. macrocentra, O. microdasys, O. monacantha, O. phaeacantha, O. pilifera, O. robusta, O. stricta, O. tomentosa and few hybrids.
Taking in account that your specimen is growing in Gran Canaria, it might be a specimen of Opuntia monacantha monstruosa.