In all the genera studied, 3-colporate, oblate to
suboblate pollen grains are arranged in tetrahedral tetrads. The apocolpial pollen wall is
composed of the exine - well developed tectum, columellae, foot layer and endexine, and
the intine. On the contrary, the septal exine is composed of fragmentary tectum, and the
two foot layers of adjacent grains are sometimes connected by columellae and endexine.
Among different infrageneric taxa only the subsect. Ledum (sect. & subgen. Rhododendron) was characterized by small sized pollen tetrads, higher 2f/D value and rugulate exine sculpture. The pollen morphological characteristics overlapped each other in all other taxa. Thus palynological features showed little usefulness in the infrageneric classification of Rhododendron, however, they gave additional support to the individual
generic status of Menziesia and Tsusiophyllum, and the sister relationship between
Rhododendron and Therorhodion.