Pollen morphology of the Rosaceae of western Canada. III. Geum
Pollen grains of eight species of Geum (Rosaceae) from western Canada were studied in the light microscope and the scanning electron microscope. The taxa included Geum aleppicum, Geum calthifolium, Geum glaciale, Geum macrophyllum, Geum rivale, Geum rossii, Geum schofieldii, and Geum triflorum. All taxa produce pollen grains in monads that are isopolar, radially symmetrical, and predominantly tricolporate. Tetracolporate grains occur especially in Geum rossii and Geum calthifolium. Grains are subspheroidal to subprolate with a circular to subtriangular amb. All taxa exhibit a well-developed chambered aperture formed by overarching pore flaps. Flaps extend over the aperture but do not join to form an equatorial bridge. The chamber of Geum schofieldii is distinct and complex, often extending equatorially along a sinuous path to the adjacent aperture. Exine is tectate, microperforate, with a thin nexine. Sculpturing is striate or occasionally rugulate and consists of ridges and valleys with microperforations on valley floors. Ridges and valleys are oriented predominantly parallel to the colpus but occasionally curve or loop near the poles. Sculpturing of Geum schofieldii pollen, is predominantly striate but exhibits a unique verrucate to rugulate pattern along the equator caused by elaboration of the sexine. Polar diameter varies from ca. 20 μm in Geum macrophyllum to 33 μm in Geum schofieldii. The distinctness of Geum schofieldii pollen supports specific status.