The phrase "entire leaf" means that the leaf's edges are smooth and not divided or with any kind of serrations or lobes. It is the opposite of a leaf with jagged or divided edges. Full definition
The tea's power is so super because entire leaves are dissolved in water rather than steeped in bags. (bodybuilding.com)
I think last season's memories are hard to erase, but it's Arsenal's entire left side that is always weak in recent times. (justarsenal.com)
Oaks have spirally arranged leaves, with a lobed margin in many species; some have serrated leaves or entire leaves with a smooth margin. (sciencedaily.com)