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.
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