Distinguish Leaves vs Leaflets: Objective Criteria

[Stephen Tashi]

TL;DR Summary

What are the objective criteria for determining whether something on a plant is a leaf vs whether it is a leaflet?

If I'm informed that a structure on a plant is a leaf with a certain number of leaflets, I can usually visualize the plant that way. But if I'm not informed about that fact, I only see leaves. How can I distinguish leaves vs leaflets?

 

[BillTre]

I'm not an expert on leaves but this is the approach I would take:
on deciduous plants (that loose their leaves seasonally) if there is a single little twig going to a single leaf surface then its a leaf. If there are little branches going from the leaf attachment point to several leaves, they are leaflets.
Its like a big leaf (evolutionarially) broken up in to several smaller leaves.

 

[Stephen Tashi]

The buds seem to be key features in the diagrams. I'm ignorant about what buds are. I think of them as the initial stages of a branch or leaf - something that would turn into a branch or the stem of a leaf and thus vanish. Yet in the diagrams the buds are still present at the base of branches and stems.

 

[BillTre]

something that would turn into a branch or the stem of a leaf and thus vanish

Buds form in the crotch between the leaf and its branch.
Buds can become branches, leaves, or flowers (buds). They don't vanish, they grow and change.