Almost always seen as the head of a compound:
三叶草 sānyècǎo (clover/shamrock),
三叶虫 sānyèchóng (trilobite, literally 'three-lobe-bug'),
三叶神剑 (a martial-arts movie title). Also the Chinese rendering of the Japanese name Mitsuba (
三叶), most famously for the heroine of Makoto Shinkai's 《
你的名字。》 (Your Name).