Pollen Morphology of Rhododendron Subgenus Azaleastrum

Pollen grains of 20 species and 2 varieties in 4 sections of genus Rhododendron subgenus Azaleastrum were examined by light microscope (LM) and scanning electron microscope (SEM) for the first time.The pollen grains of subg.Azaleastrum are arranged in tetrahedral tetrad,the tetrad diameter ranges from 3585 μm to 6072 μm.Asingle pollen is spheroidal or subspheroidal,with tricolporate aperture,which shaped as half colpus due to two neighborly grains of tetrahedral tetrad link together,and viscin threads can be seen on the pollen surface.The exine sculptures of subg.Azaleastrum can be divided into scabrid,compact granulate and unconspicuous granulate types in SEM.The exine sculptures are different among different sections in subg.Azaleastrum and therefore can provide some proof for identification of some species in Rhododendron.