Gotelli M. M., Scambato A., Galati B., Kiesling R., Pollen development and morphology in four species of Pterocactus (Cactaceae), Annales Botanici Fennici, 2009, 46(5):409-415, doi: 10.5735/085.046.0505
A study of anther and pollen development in four Pterocactus species using light and scanning microscopy. It describes anther wall tissues, microspore formation, bicellular pollen and traits of its wall. It compares differences between P. australis, P. araucanus, P. hickenii and P. valentini, written as P. valentinii in the paper.