Leaf cuticular morphology links Platanaceae and Proteaceae

The leaf cuticular morphology of extant species ofPlatanuswas investigated using light and scanning electron microscopy. All species are shown to possess trichome bases of the same type as those commonly found in Proteaceae. Of particular significance are compound forms that consist of an annular surface scar associated with more than one underlying epidermal cell. These are found on the adaxial leaf surfaces of all species ofPlatanusand are also clearly evident on the abaxial surface ofPlatanus orientalis. This type of trichome base is therefore interpreted as the first detected nonreproductive morphological synapomorphy linking Proteaceae and Platanaceae. Also, the laterocytic, sometimes paracytic, or anomocytic arrangement of subsidiary cells inPlatanusis distinct from the general state in Proteaceae, which is brachyparacytic and presumably derived. InBellendena, possibly the most basal genus of extant Proteaceae, subsidiary cell arrangements resemble those ofPlatanus. These results are discussed with respect to leaf fossil records of Proteales, where it is concluded that the combination of brachyparacytic stomata and compound trichome bases is strong evidence for Proteaceae.