Forget the botany books. Here’s the real test: if you hold a zucchini and think, “This feels like it could be a squash,” you’re right. If you eat it raw in a salad, it’s a squash acting like a cucumber. If you grate it into bread, it’s a squash pretending to be a dessert.
Squash Zucchini Benefits at Amy Beasley blog
The most reliable clue is the stem. Zucchini has a pentagonal (five-sided) stem, while cucumbers have a round one. Yes, I just gave you a reason to examine your produce like a detective. You’re welcome.
Also, if you cut it open and see a star-like pattern of seeds in the middle, congratulations. You’re holding a squash. And you’re probably about to make a really good stir-fry.