Cryptic andromonoecy in Tilia japonica implicated by flower abortion

Tilia japonica Simonkai has morphologically perfect flowers with stamens and a pistil. However, some flowers fall without developing into immature fruits. We clarified that: (i) the flower abscission is a facultative abortion, (an abscission layer was observed at the base of the stalk of aborted flowers); (ii) fallen flowers have functional stamens (the flowers are protandrous and they had shed germinable pollen grains before the flower abscission); and (iii) fallen flowers have a non-functional pistil (they were abscised before stigma opening). The aborted flowers were functional male flowers, although they were morphologically perfect. Hence, the functional sex expression of T. japonica is andromonoecous having both perfect and male flowers within an individual tree.