Studies in Montia L. and Claytonia L. and Allied Genera

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Abstract
The pollen morphology of several genera in Portulacaceae is described. Particular attention has been paid to the genera of the subfamily Montioideae, as a stage of continued monographical studies. Among genera especially dealt with are Claytonia, Montia, Crunocallis, Naiocrene, Neopaxia, Mona, Maxia, Limnalsine, and Montiastrum. In the taxonomical treatment of these genera the pollen morphology has proved to afford many important additional characters. The pollen grains of Claytonia are distinguished from those of the remainder in being 3-colpate. The grains of the Claytonia-type have many similarities with those of Lewisia, a genus of the subfamily Portulacoideae. The other genera of Montioideae have pantocolpate pollen grains. Among these genera several different pollen types are distinguished, chiefly with regard to the sexine structures and the aperture membranes. The Montiastrum-type is especially interesting, with tholate grains, a particular pollen type not met with in any other genus in the family. The pollen morphology of some genera in the Portulacoideae is also treated. In some species in Calandrina and Talinum pantotreme pollen grains are observed with apertures transitional between pori and colpi. The apertures of the pantotreme grains are arranged in characteristic patterns. Particular attention has been given to the variation of the pollen morphological characters. This variation has been examined with regard to the differences between different populations of the same species as well as between different species. The greatest variation has been observed in the shape and size of the grains. The structure and sculpture and thickness of the sexine and the aperture membranes are less variable. Some polyploid taxa are connected with the occurrence of pollen grains with divergent and varying aperture numbers. In a survey of the genera the taxonomical results of the investigation are presented with particular regard to the pollen morphology. The new genus, Maxia Ö. Nilss., is described. One new species, Montia clara Ö. Nilss., is described and some new combinations are made. Pollen morphological diagnoses are given for 46 different taxa. The aperture conditions for 96 different species are presented.

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