I've never seen a living specimen of Madagascan lace plant Aponogeton madagascariensis but I found this pressed specimen in the herbarium of Durham University's School of Biological and Biomedical Sciences. I suspect it's a very old specimen as it still bears an old Latin name for the genus, Ouveranda. These look like skeleton leaves but in fact they are intact - during the final stages of development of the expanding leaves of this aquatic plant the cells between the veins die, during the process of programmed cell death (apoptosis) leaving a network of veins surrounded by living photosynthetic cells. The development of the leaf has recently been studied in great detail and you can read the scientific paper from the American Journal of Botany that describes the process (which also includes photos of the whole, living plant) by clicking here.
In this close-up of a portion of the pressed leaf you can see the ladder-like arrangement of leaf veins that are surrounded by photosynthetic tissue. Apparently this plant is a popular but challenging species to grow for tropical aquarium enthusiasts and you can read an account of its cultivation here.
