Its pretty common for some varieties. I plant about 5 seeds x 60 varieties every year and usually see one or two a year. My hot peppers had a bunch of triplets this year.

So spiced_ham this has happened to you before eh? Maby the odds are more 1 in 1000, I'm curious if these plants have more energy and grow faster with the extra leafs.

There is alot of variability in sprouts due to seed weight, and who knows the many ways a home grower can screw up his own seedlings, so a lone tricot would have to be a super plant or a dud to be noticed. I haven't noticed any such difference in the tricots unless maybe they are a bit smaller, but that might just be visual with three 'leaves' coming out of a normal sized seed

I planted about 350 seeds at the end of March. I had one seedling with three cotyledons and another with one normal cotyledon and one cotyledon which was a Siamese twin (y-shaped).

As it happened, the three-cotyledon seed was culled -- I think because its fellows of that variety were larger. However, its three-cotyledon status should not be blamed; many things this year were not ideal, including having my appendix removed just when I should have been potting up.

[Yeah, that is way too many seeds, but I'd never grown tomatoes from seed before -- or grown anything in the basement under lights -- and didn't expect much success. Several dozen of the better-looking extras were donated to a charity plant sale.]