Leaf abcission scars/lumps

Just curious, does anyone know why the stems of habitual leaf-dropping plants (classic example: Plumeria spp. and long-stemmed Crassulaceae) become so lumpy from the progressive accumulation of decommissioned “leaf-attachment-point warts” and their associated scars? I suspect it may just be the result of “sloppy” evolution (plant stuck at local optima; physiologically difficult to resorb the lumps) but I am unsure whether this is actually the case; I could not find any published research on the topic.

Thanks

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What would be the evolutionary advantage of smoothing the scars? The plant doesn’t care what it looks like!

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Tissue optimization? After all mammal scar tissue is known to be slightly inferior to uninjured stuff structurally.

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Protection from pests that might use the former attachment site as an easy way to enter the plant maybe? I’d imagine scar tissue is a lot tougher to get through than vascular tissue

It’s not “scar tissue” in the plant, it’s the original tissue that formed as the leaf did.

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