Hi Yuki, that would indeed be possible, but the size of the stem is so small, that a 4-sided (maybe even a 3-sided) cylinder, set to Shade Smooth would probably be better, because the computations, necessary to calculate the direction of the planes would be more ‘expensive’…Also: the flowers will be mostly seen from above, which would be a strange perspective for a plane stem.
And if the stem is curved, then circling the camera around the flower would look really weird, because the curvature wouldn’t change.
Lastly, for a plane version of a stem to appear round, you would need a lighter and darker side, depending on the sun light, which would change when the camera moves around.
All this could be compensated by using a lot of math, but it would not be worth the trouble and end up using more resources the using a low-poly cylinder.