The peculiarity that clover leaves can be found very close to an important landmark, the Mysterious Machine. The important device that you spend much of the initial game trying to fix has a little clover growing right next to it.
To harvest the leaves you will need a cutting tool, and after that it is a simple matter of cutting them and adding the fallen leaves to your inventory by picking them up.
Now that you know how to find a clover leaf in Grounded you will be able to keep this item in your inventory so you never miss it. Luck!