Pollen morphology of Raphionacme (Periplocaceae)

The pollen morphology of all 35 species of Raphionacme Harv. (Periplocaceae) has been studied. All species of Raphionacme, except R. abyssinica Chiov. in which pollinia occur, are characterized by pollen grains arranged in tetrads, the grains may be arranged tetragonally or rhomboidally. Pores are restricted to the junction area of adjacent grains, and are sometimes covered with a layer of exine material. Exine is smooth and covered with a thin electron-dense layer. Granular endexine is present above the intine. The internal walls are perforated and have the same structure as the exterior wall. Pollen grains are starchless. The pollen grains of Raphionacme are uniform in structure and cannot be used to identify species