Little leaflets growing out of petiole

That's a nice mutation you got there! it's probably like the more known mutation of growing buds on fan leaf petioles but in this case it's an extra leaflet! This may prove as a beneficial mutation since leaves are the plants' main source of energy (photosynthesis) and more leaves will produce more energy but in the other hand it may cause an issue with air circulation and risk mold. anyways this is a mutation in the plant and should not lower yield or affect the plant badly just keep an eye under those overlaying leaflets for any signs of pests/fungi. Good luck and happy growing :)

Yes, cannabis plants will do some strange things at times, but it is nothing to be worried about, they are just being "individuals". For a collection of photographs of multiple strange leaf growths (like buds growing on leaves!) have a look at my diary "Holy Mackerel" for an insight. You will also find pictures of "hermies", both male and female primordia (pre-flowers) and the exposed roots of a three week old seedling to get an idea as to why deep watering is so important and why watering seedlings with a sprayer is just not adequate, amongst other bits of weird and wonderful cannabis conundrums! Hope this helps,..... Organoman.