Calcium oxalate and medullary architecture in Xanthomaculina convoluta

The anatomy of Xanthomaculina convoluta shows adaptation to a vagrant life form and to the moisture conditions of its habitat. The differential swelli ng of the irregularly thickened upper cortex and the medulla, in addition t o the rigid medullary structure, due to the deposition of calcium oxalate, allow orderly hygroscopic thalline movements. The architecture of the medul la appears to be closely related to masonry-like arches where the material is only stressed by compression and the stresses are distributed at the hin ges. The possible role of crystalline medullary deposition as a radiation r eflector is also suggested. (C) 2000 The British Lichen Society.