Early Floral Development of Endangered Euryodendron excelsum (Ternstroemioideae: Theaceae)

The floral development of a critically endangered plant Euryodendron excelsum from Ternstroemioideae (Theaceae) has been observed under scanning electron microscope (SEM) for the first time. The flower of E. excelsum is bisexual and teleianthous. Five sepal primordia are initiated 2/5 spirally and arranged in one whorl when mature, and so are petals. Sepals and petals are initiated in the same order either clockwise or counterclockwise in the same flower. The androecial part is a ring primordium in the beginning. The first five stamen primordia are initiated on this ring primordium at antisepalous positions and then other stamen primonlia appear on two sides of each of the first five primordia. Finally a total of 25 stamen primordia are initiated from the ring primordium and arranged in one whorl but could be grouped into 5 fascicles. Three sequentially initiated carpels compose an ovary which has an axile-central placenta with three locules and a truncate and indehiscent stigma. The floral development of E. excelsum is distinctly different from plants in Theoideae.