Abstract: In order to understand the ultramicroscopic features of mature pollen grains of Habenaria sagittifera，transmission electron microscopy was applied to characterize the pollen grains in the massulae of this species at anthesis. （1）Pollen walls on the surface of the massula consisted of more layers，including tectum，baculum，nexine-1，nexine-2 and intine，while pollen walls within the massula was comprised of fewer layers，lacking tectum and baculum.（2）Both vegetative and generative nuclei in mature pollen grains were predominated by highly condensed chromatin，which occupied over half of the inner space of the nuclei.（3）The pollen grains did not contain lipid bodies，starch grains，or storage proteins，indicative of the absence of macromolecular storage reserves. In summary，the structural difference between walls on the surface of the massula and walls within the massula，the highly condensed status of the vegetative nucleus，and the absence of macromolecular storage reserves were the most noticeable ultramicroscopic characteristics of the mature pollen grains of H. sagittifera.

Key words: Habenaria sagittifera, mature pollen grain, pollen wall, chromatin, pollen storage reserve