In Yoshi's Island, the Super FX 2 chip is used to perform smooth sprite rotation. However, it is limited to rotating 64 8x8 pixel sprites at once. For cases where the chip is already busy rotating other objects, the flowers have a fallback state where they animate less smoothly.
As pointed out on the bottom of the post, this was found by YouTube user Samb (), who only discovered this by datamining, seeing that the flower disappeared from the Super FX 2 memory, as the effect is extremely subtle! Thank you very much for your inquiry!
It is never 64 separate objects, but rather a small amount of large objects that need up to 64 small sprites to put them together. For example, the rotating spikes in castle levels take up the entirety of the Super FX 2 space. as shown below. Thank you very much for your inquiry!
Some objects (e.g. rotating buckets) have no non-Super FX fallback states. The game is designed so they never appear in large groups to overload the chip, but if they do (with glitches), they will simply despawn! Thank you very much for your inquiry!