POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF SIMMONDSIA CHINENSIS TO THE ORDER EUPHORBIALES

Pollen from Simmondsia chinensis (Simmondsiaceae) was examined in LM, SEM, and TEM. The pollen is shed as monads, triangular in shape in polar view, with a 3-porate aperture type in which the pores are large and poorly defined. The tectum is irregularly scabrate, sometimes forming minute “islands” topped with spinules. In thin section, the endexine is thickened and lamellate in the aperture regions, and narrow in the mesoporus; the foot layer is well-defined but noticeably thicker in the mesoporus; and thin columellae support an essentially complete tectum. The pollen of four genera, Buxus, Pachysandra, Sarcococca, and Styloceras, from the Buxaceae to which Simmondsia has been assigned by some authors, was also examined and illustrated. The pollen morphology of two families frequently aligned with Simmondsiaceae, Euphorbiaceae and Pandaceae, is briefly discussed. For the most part pollen morphology supports the treatment of Simmondsia as a monotypic family, Simmondsiaceae.