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, I suspect the answer is more common than it appears at first glance.  Three possibilities, all of which assume that the 3 kinds of squash are from 3 different vines, 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 with the image of a relatively small area in your garden. 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 yarn loosely tied to the vine.

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

- When cleanup, is complete, how many piles of vines do you have?  One or three?  (My bet is on 3.)

I will do as you suggested and tie some different color ribbon to each of the vines these three different squash are growing from. And I will be very careful with my end of year clean-up to see what comes of tracing down the source of each vine. To tell you the truth though, I really hope you're wrong about there actually being three different plants. Only because it would be way more interesting to figure out how three very different looking squash could be growing on one plant :-)

All of the seed I planted this year are from new packages but from two different places.

I'll let you know what the results are, along with more pictures after harvest.

Kirt,

That should be fun.  I’ll anxiously await the results!