A comparative flower and fruit anatomical study of Quercus acutissima , a biennial‐fruiting oak from the Cerris group (Fagaceae)

A developmental series of flowers and fruits of Quercus acutissima (subgenus Quercus section Cerris ) was collected over a growing season and examined for an intersectional, comparative anatomical study. Pistillate flowers of the current growing season, each consisting of a pistil with three long, slightly recurved styles, six tepals, and an inconspicuous ovary subtended by a few cycles of cupule scales, emerged in early May, were pollinated by mid‐May, and then were quiescent for the remainder of the growing season. Flowers from the previous growing season resumed growth in mid‐May, each forming three locules delimited by septa in the ovary, with two bitegmic, epitropous ovules developing in each locule. Mature embryo sacs were present by mid‐July of the second growing season, although embryos were not observed until early August. Fruit maturation was complete by late September. Features that have not been described previously for the section Cerris include early‐lignifying endocarp trichomes, persistent septa, and leaf primordia buttresses on the embryo. A comparison of flower and fruit developmental features with sections Quercus sensu stricto and Lobatae revealed a mosaic of shared features among the three sections.