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The size of the staminodes and ring stamen of Couroupita guianensis (cannonball tree) grown in the Nonthaburi province, Thailand as well as some characteristics of their pollen were investigated. The staminodes were clearly larger than the ring stamens. This finding is at variance with other previous studies. Viability staining showed that almost all the cannonball tree pollen from hood staminode were not viable but about 85% of the ring stamen pollen were viable. When both types of cannonball tree pollen were cultured on modified Mercado medium, hood staminode pollen did not germinate whereas the sucrose concentrations in the medium had a promotive effect on germination of ring stamen pollen. About 65% of the ring stamen pollen germinated on the medium supplemented with 20% sucrose. These pollen studies were in agreement with other similar studies on cannonball trees, suggesting that the relative sizes of the male reproductive organs of cannonball trees may not be related to fertility of their pollen.