Comparative pollen morphology of the styracaceae

Pollen representing twenty-three species in all eleven genera of Styracaceae was examined by combined light, scanning and transmission electron microscopy. A comparative examination of the morphological features of the grains was conducted in an attempt to evaluate the importance of pollen morphology to the systematics of the family. Pollen morphology of the Styracaceae is rather uniform, with few variable features. Grains of nearly all examined species are solitary, mediumsized, radially symmetrical, tricolporate with lalongate endoapertures each with an equatorial bridge, and a tectate-perforate-columellate exine. The stratified exine has four consistent layers, including a well-developed tectum and an endexine that is often internally thinly fragmented along the mesocolpi and thickened under the colpi. Although the pollen of the family is relatively uniform, subtle variation is present, particularly in sculpturing type, where intertwined rugulate-reticulate, transitional fossulate-foveolate, finely rugulate, reticuloid, and weakly crotonoid exines occur. Outer tectal surfaces are smooth, granulose, microspinulose, beaded and banded. The large genus Styrax encompasses much of the pollen morphological variation observed within the family. Grains of Parastyrax are occasionally 4-aperturate and have especially thick exines. Pollen morphology of the Styracaceae is similar to that of Theaceae, with both families possessing basically tricolporate grains with a finely perforate or reticulate sculpturing pattern and a smooth outer tectal wall. It is suggested that within both families specialization has led to similar fossulate-finely rugulate and foveolate-fossulate sculpturing patterns with beaded or banded outer tectal walls.