Systematic Significance of the Development and Anatomy of Flowers and Fruit of Quercus schottkyana (Subgenus Cyclobalanopsis : Fagaceae)

The developmental process of flower and fruit production was studied for the first time in Quercus schottkyana (subgenus Cyclobalanopsis) and compared with other species of Quercus and related Fagaceae. Four main developmental periods were recognized, and standard embryological features such as basic type of anther wall formation, simultaneous cytokinesis of microspore mother cells, tetrahedrally arranged microspore tetrads, and two‐ to three‐celled pollen grains. Polygonum type of embryo sac development, delayed fertilization, and free nuclear endosperm were observed in Q. schottkyana and confirmed to be plesiomorphic. In Q. schottkyana, the primary archesporial cell divided into megaspore mother cells without forming a primary parietal cell, a condition that may be derived in Fagaceae. Another possibly derived state observed at an early ovule stage was a pseudocrassinucellate nucellus, defined by ovule epidermis giving rise to the subdermal layer (parietal layer) and archesporial cells directly developing into megaspore mother cells. During seed development, the funiculus was sessile and attached to the middle of an extremely compressed placenta; thus the apical position of aborted ovules in Q. schottkyana can be attributed to the elongation of both the placenta and the funiculus. Comparative studies suggested that the large size of the style at pollination, a hemianatropous ovule, and a sessile funiculus are likely synapomorphies of the genus Quercus. The new data on Q. schottkyana confirm the hypothesis that evolutionary novelty in the development and anatomy of Quercus flowers is mostly found in terminal clades. Two autapomorphies, lateral position of the hilum and lateral originated primary vascular bundle in the seed coat, potentially distinguish subgenus Cyclobalanopsis from other species of Quercus.