The term 'spiny succulent plant' can be summarized by two crossword solutions: CACTUS (6 letters) and ALOE (4 letters). Cacti are a family of plants native to the Americas, characterized by their thick stems and spines. Aloe is a genus of succulent plants native to Africa, with some species also found in other warm climates. Both cacti and aloe plants are known for their ability to store water in their leaves, making them well-suited to arid climates.