Hello there! I would be happy to help you tell cilantro and parsley apart for your family barbecue marinade.
First, look closely at the leaves. Cilantro leaves tend to be more rounded, fan-shaped, and feature soft, scalloped edges. On the other hand, flat-leaf parsley leaves are pointed, sharper, and look a bit more like tiny maple leaves with jagged edges.
Another visual clue is the color and growth pattern. Cilantro usually has a brighter, lighter green color and grows in a more delicate, sprawling bunch, while flat-leaf parsley tends to be a darker green and grows in flatter, denser clusters. If you are ever in doubt, a quick gentle pinch to smell them will instantly clear up any confusion since cilantro has a distinct citrusy aroma. Good luck with your barbecue!