Abstract: Pollen grains of 6 genera, including 36 species, of the Betulaceae, were examined under LM, SEM and TEM.Their morphological characters are described and three types of pollen are distinguished here. The evidence from pollen morphological characters does not support Hutchinson's (1973)and Dahlgren's (1983)treatments which divided the Betulaceae into two families: Corylaceae ( including Corylus, Ostryopsis, Carpinus and Ostrya) and Betulaceae (including Alnus and Betula). The author agrees with Abbe's (1974)division of the Betulaceae into three tribes with one modification that Ostryopsis is transferred from the tribe Coryleae to the tribe Carpineae. The limits of the three tribes presented here are the same as Kuprianova's (1963) treatment in which she divided the Betulaceae into three families. It is more reasonable to treat Kuprianova's families as tribes. Pollen morphological characters of the three tribes of the Betulaceae are described as follows: 1. Tribe Betuleae (including Alnus and Betula): Pollen grains are triporate or stephanoporate and oblate, suboblate or spheroidal. Sometimes the exine has arci and the ektexine thickens in the apertural region; the sculpture of exine is slightly rugulate under scanning electron microscope (SEM) ; the exine structure is four-layered: tectum, columellae, footlayer and endexine. The columellae are columellate, the endexine thickens in the apertural region and sometimes it is separated from the footlayer to form vestibulum. 2. Tribe Coryleae (only Corylus): Pollen grains are triporate and suboblate. The exine has no arci and the ektexine does not thicken in the apertural region; the sculpture of exine is slightly rugulate under SEM; the exine structure is five-layered: granular layer, tectum, columellae, footlayer and endexine. The tectum is vovered with a granular layer, the columellae granular and the endexine thickens but is not separated from the footlayer in the apertural region. 3. Tribe Carpineae (including Ostryopsis, Carpinus and Ostrya): Pollen grains are mostly triporate and suboblate. The exine has no arci and the ektexine does not thicken in the apertural region; the sculpture of exine is slightly rugulate under SEM; the exine structure is five-layered which is the same as those of the Coryleae. The tectum is covered with a granular layer, the columellae are columellate and the endexine is neither thickened nor separated from the footlayer in the apertural region. The operculum exists on the top of aperturemembrane.

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Key words: Betulaceae, Pollen morphology