APOMIXIS AND SEXUALITY IN THREE SPECIES OF AMELANCHIER, SHADBUSH (ROSACEAE, MALOIDEAE)

We used Nomarski differential interference contrast microscopy of cleared, whole ovules to examine megasporogenesis and megagametogenesis in tetraploid (N = 34) individuals of three species of Amelanchier in Maine. Amelanchier canadensis and A. stolonifera conform to the general pattern of apomixis in the Maloideae by being aposporous and by frequently forming more than one megagametophyte per megasporangium. These species are also pseudogamous; both self and foreign pollen elicit fruit set. Amelanchier bartramiana follows a sexual pattern by producing a triad of megaspores and almost always only one megagametophyte per megasporangium. This boreal shrub, strikingly distinct morphologically and in its habitat preference from other North American species of the genus, is primitive in its sexuality and self‐incompatibility relative to other species we have studied.