Pollen morphology of the Rosaceae of western Canada. II. Dryas, Fragaria, Holodiscus

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Abstract
Morphology and geographic variation of pollen grains of three genera of the Rousaceae (Dryas, Fragaria, Holodiscus) of western Canada were studied using the light microscope and scanning electron microscope, Dryas spp. pollen in tricolporate with a weakly developed fusiform aperture in the colpus, which upon expansion of the grain becomes a large rectangular opening. Sculpturing consists of ridges and valleys (striate or rugulate), the latter containing perforations, which grades to a network of riges and perforations (reticulate) at colpus margins. Ridges are parallel to the colpus or form looping patterns. Dryas integrifolia and Dryas octopetala pollen in silicone oil usually are larger than those of Dryas drummondii, Fragaria spp. pollen is tricolporate with a well-developed complex equatorial aperture. Fragaria chiloensis and F. vesca exhibit a lobed and equatorially extended endoaperture, which is overarched by sexine, Fragaria virginiana usually has a less distinct endoaperture. Fragaria species have a fusiform colpus operculum. Sculpturing consists of nonasastomosing ridges parallel to the colpus and valleys containing obscure microperforations. Holodiscus discolor pollen is tricolporate. Sculpturing is striate to reticulostriate, consisting of ridges and valleys with perforations. A distinct zone, either lacking ridges of densely packed ridges, borders the colpus.