Pollen-ovule ratios in seven species ofVaccinium(Ericaceae) and stamen structure inVaccinium myrtilloidesandVaccinium vitis-idaea1This article is part of a Special Issue entitled “Pollination biology research in Canada: Perspectives on a mutualism at different scales”.

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Pollen-ovule (P/O) ratios were determined for five Vaccinium species (Ericaceae) native to eastern Canada (Nova Scotia: V. angustifolium, V. boreale, V. caespitosum, V. corymbosum, V. uliginosum), one in western Canada (Saskatchewan: V. myrtilloides), and one (V. vitis-idaea) from both provinces. Pollen, released at maturity as tetrads, was converted to total pollen grains per flower to yield P/O ratios ranging from 238 (V. caespitosum) to 2008 (V. vitis-idaea), but 736 for the latter in Saskatchewan. These P/O ratios are indicative of facultative autogamy to facultative xenogamy. Additionally, the structure of mature stamens and pollen tetrads was studied in V. myrtilloides and V. vitis-idaea. Each anther was functionally bilocular; had a single-cell thickness (i.e., epidermis) with regularly occurring papillae; lacked an endothecium; and possessed two distal, hollow tubules each terminating in a pore. Overall pollen grain viability was 76%–97% (V. myrtilloides) and 51%–93% (V. vitis-idaea), with about 20% of tetrads having only 1–3 grains viable, and 12% and 27% of tetrads entirely nonviable in V. myrtilloides and V. vitis-idaea, respectively. Pollen tetrads occasionally were connected by a sticky substance resembling pollenkitt, but viscin threads were absent. One instance of precocious (in situ) germination of tetrads was recorded within anthers of V. myrtilloides.