Pollen morphology and exine ultrastructure of selected species of Waltheria L. (Byttnerioideae-Malvaceae)

- Record of exine with 4 layers and intine with columellate-like structure
- Pollen differences on heterostyle species
- Suprareticulate exine in pollen grains of longistyle morph of Waltheria
- Pollen morphology of some representative of Byttnerioideae subfamily

The pollen morphology of five species: Waltheria albicans Turczaninow, Waltheria brachypetala Turczaninow, Waltheria cinerascens Auguste Saint-Hilaire, Waltheria martiana Bentham ex J.G. Saunders, and Waltheria viscosissima Auguste Saint-Hilaire were studied by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), focusing on apertural type and exine. Pollen grains are medium to large, isopolar, oblate spheroidal to prolate spheroidal, 3(-4)-5(-6)-zonocolporate, costate, and fastigiate. Exine ornamentation is microreticulate, homobrochate, suprareticulate (longistyled morph), and microechinate to echinate (brevistyled morph). Sexine thickness is equal to or greater than the nexine. In TEM, the sexine consists of four layers, having an inner sexine 1, and outer sexine 4. An ultrathin section of exine revealed a columellate-like intine on pollen grains of W. cinerascens.