Charles Darwin's early sketch of an evolutionary tree (or a coral), drawn in 1837 (A). Marine organism (Bossea arbignyana) collected by Darwin and classified by him as a coral ("family Corallinae"). Later it was discovered that this "coral-like" inhabitant of sea waters (B) is a red alga (family Corallinaceae, Phylum Rhodophyta). Red coral (Corallium rubrum), which grows on rocky sea bottom either in the depths or in dark caverns (C). This wide-spread species, which is found mainly in the Mediterranean Sea, was known to Darwin and possibly served as a model for his diagram (see Figure 4) [adapted from ref. 22].