Pollen morphology of the genus Aesculus (Hippocastanaceae)

Abstract

The 13 species of Aesculus recognized in a revision by Hardin (1957, 1960) and two species of Billia were investigated by LM and SEM, and three species of Aesculus by TEM. In addition to the species recognized by Hardin four more species of Aesculus (A. bushii, A. megaphylla, A. rupicola and A. polyneura) can be distinguished on the basis of their pollen characteristics. Four pollen groups of Aesculus species are described. The data of Hsiech (1979) on the polymorphism of the sect. Calothyrsus were confirmed. In addition to a few pollen features which are discrete one, a continuum or more complicated regular varieties was observed with respect to many pollen characteristics. These patterns are not reflected in any typology or classification and are usually ignored in systematic investigations, and consequently also in the evolutional interpretation of the morphological data. This investigation of the regular pattern in the variety of pollen aperture arrangement allows an assumption about the mechanisms of pollen aperture determination and the origin of variety.