Well, that certainly is puzzling! It’s true that occasional random changes can occur on an individual plant via spontaneous mutation. But because this is a vegetable garden with supposedly just two squash plants… I still suspect the answer is more common than it appears at first glance. Three possibilities, all of which assume that the two kinds of squash are from two different vines (different plants), are these:

1- You added compost in which some squash seeds survived.

2- If seeds saved from last year were planted, each of this year’s seedlings could produce squash different than the original.

3- And, even if all the seeds planted this year came from a newly obtained packet, it’s possible that several “rogue” seeds were inadvertently included.

Okay, it’s obvious that your question can’t be answered using these images from your garden - the vines are too closely intertwined. So, to resolve this mystery, perhaps a simple scientific experiment will provide the answer. Here’s what I suggest you do:

- While the squash are still attached to the vine, mark each origin with a piece of colored yarn loosely tied to the vine. Use two different color yarns to mark the yellow or the orange fruits respectively.

- During your end-of-the-season cleanup, carefully remove the tangle while keeping the yarn markers in place and the vines intact.

- When cleanup is complete, you should expect to have two piles (one for each plant). But how many piles of vines do you actually have? (I’m betting 3) And more importanly, how many vine piles are there with both colors of yarn attached? One or two? (My bet is on none.)

If you can do this experiment please let us know what you discover if it not what I just predicted - (mention Question #363431).

Thanks so much for the great question and puzzler!