Plant has only one cotyledon

So my plant has only one cotyledon and its growing slowly but it's growing. The cotyledon seems like it was burnt or something (note this is my first time growing and it's outdoors and no nutrients).
I have another plant that is growing just fine and is about 2x this plant I'll post some pictures of it.

It may have been nibbled off. If it is a genetic issue it could be on the runty side.