Virtually all citrus seedlings have thorns. I don't necessarily know the scientific explanation; only the fact.

Thanks Johnmerr, yes, I have lemons and limes and they are thorny. Somehow, the genetics of a branch that is grafted into new root stock apparently express differently than on its native roots. I know some root stock does well in certain soil and climates but not in others so it's nice that grafting helps us grom plants we couldn't otherwise grow but it amazes me to see a fruit produced by thornless wood grow a VERY thorny offspring.

Grafted citrus varieties are created from extremely mature wood. Usually this wood is nearly thornless. I know this is true for oranges for example.

Juvenile growth in citrus (from seed) is thorny in most varieties. This may be a seedling's way to protect itself somewhat from grazing.

Anyway, once your tree reaches a certain height (I have no idea how high), that highest growth may eventually have smaller to no thorns. But it will be very high up in the tree.

It all has to do with the nature of how citrus wood changes its appearance and characteristics from juvenile to mature over time. Juvenile wood is not able to flower and produce fruit either.

John has given you the basics & Dave has given you the exact explanation - has to do with where the budwood was cut for the grafted trees, John. What you're seeing is very normal for any citrus seedling - Calamondin, Lemons, Oranges, Pummelos, etc. No surprise here.

Patty S.

It also applies to all other trees. They grow differently at youth and maturity whether it is a thorn tree or not. If you got the seedling from the nuclear embryo it should grow true to the mother plant and will have no trifoliate leaves.

Fantastic responses! I think I will be able to sleep at night again and I don't need to wonder if we and Mendel have missed some important genetics research opportunities.

Thanks folks!

Yes, no need to worry at all, John! Some citrus cultivars can be wickedly thorny when young, then become completely thornless. I was really shocked to see what were about 2" long thorns on my Yosemite Gold mandarin of all things. And, this is a grafted (but young) tree. It has a big growth spurt, and on the new branches there were thorns that would make your knees weak, I was really surprised, as it's "cousins", the Shasta Gold and Tahoe Gold mandarins were not sporting these enormous thorns. It's just a young citrus's way to protect itself and its tender new growth from animals wishing a yummy meal. Seedlings will always be more pronounced in their thorniness as you don't see this "mature budwood" phenomena that you do with grafted citrus. Usually. But, not in the case of my Yosemite Gold mandarin, which is definitely grafted!

Patty S.

Patty,

Maybe what you had was a water sprout. Quite a few citrus varieties have thorns on water sprouts; some water sprouts of my Meyers have huge thorns; but if you cut them back to the general canopy level, they revert back to normal growth, normal leaf size, and normal thorns.

While we are discussing thorns on citrus, maybe we should just mention for newly budding citrus growers that sometimes grafted citrus will develop very thorny growth from the very base of the tree where the rootstock is. The leaves will probably be different from the new leaves on the rest of the tree. These should be trimed off close to the trunk to prevent them from robbing nutrients from the fruit-bearing grafted part of the tree.