ThornLESS is not thornFREE. the same applies to seeds.

I had figured as much, but had found in a number of places claims that thornless trees are thornFREE trees. I figure since every seed grown I've ever worked with has been pretty thorny that thornless just meant less. Although both of mine have had no thorns until their recent growth spurt.

Older branches tend to have less thorns, but my water sprout branches always tend grow some protection.

Clear case of bait and switch by mother nature.

I've noticed the same ken. Tropic, ha. In all seriousness though, I'm curious if there's something culturally that encourages the growth of thorns. Both of my kumquats have been totally thornless until this recent growth spurt where I'd say a good number of branches have little hidden thorns. I'm curious if the cold might have something to do with it as it has been both brighter and colder this year than previous. In the past their room doesn't drop below 60, this year it's regularly dropped below that at night.

So seriously speaking. Aging in plant is quite peculiar. The leaves forming at the top are chronologically youngest but ontogenetically oldest - The cells on top are results of many cell divisions. That is why node count is important for fruiting/flowering since the oldest cells are actually near top.

So bottom of the trunk has the youngest cells ontogenetically. Immature you may say . So much so that cells closer to soil line can become anything they want - they can become roots (aerial roots) or shoots easily. So any shoot coming out of the bottom is like a plant that is just sprouted from seed genetically speaking and thus more likely to behave like a seedling. Same is true for cells in root just under the soil line. They can give rise to shoots (suckers) and genetically young roots.

As a side result of this the above observation is used to advantage in bonsai. If done right one can aggressively prune the shoots or the roots and expect an explosive response. The key is timing it. In case of shoots it is easy to observe it. When a plant is topped or a huge branch is accidentally damaged the plant activates all those genetically young cells you get clusters of new branches all along the stem. But the same can happen when you prune roots aggressively. I can take a healthy ficus in summer and cleanly slice of 90% of the roots and leave the thick portion of what looks like stem under the soil. And in a few weeks the soil will be full of fine roots. Of course, not all plants will respond in the same way. Some respond more enthusiastically than others.