Complex sentence: Most "Cucurbita" species are climbing annual vines and are mesophytes (requiring a more or less continuous water supply), while the perennials grow in tropical zones and are xerophytes (tolerating dry conditions).
Split into simpler sentences: Most "Cucurbita" species are climbing annual vines and are mesophytes (requiring a more or less continuous water supply). The perennial species grow in tropical zones and are xerophytes (tolerating dry conditions).