摘要：Purshia spp. (Rosaceae) comprise a widespread western North American species complex that is important as landscape dominants, wildlife habitat, browse for wild and domestic ungulates, and seed reserves for small mammals. This study examined aspects of the phenology, compatibility, pollination biology, and progeny fruit characteristics of multiple accessions of bitterbrush (Purshia tridentata), as well as a putative hybrid between bitterbrush and Purshia stansburiana. Except for open- and wind-pollination treatments, mass pollination was accomplished at anthesis within white paper sacks, which were used to isolate treatment branches. Bitterbrush appears to be largely self-incompatible and requires some agent, either wind or animal, to effect pollination. While the majority of pollination of bitterbrush flowers is undoubtedly accomplished by insects, some pollination by wind is possible (ambophily) when shrubs are closely spaced, as flowering is fairly synchronous. Flower duration varied among shrubs, but generally lasted from 12 to 24 hours, depending on weather conditions. Flower development stage had little effect on fruit set, indicating prolonged stigma receptivity. Populations of bitterbrush exhibit considerable interfertility, as well as substantial hybridization with congeners. Intrapopulation crosses were only slightly more successful than interpopulation crosses. One of the populations analyzed exhibits characteristics consistent with its putative hybrid nature, having more than one pistil per receptacle, smaller but longer fruits, and a greater reliance on insects for pollination. Both maternal and paternal effects are important in fruit development. Taxonomic relationships within the complex are discussed.Las especies del género Purshia abarcan un amplio complejo de especies del área occidental de Norteamérica, las cuales son importantes como dominantes del paisaje, hábitat de la vida silvestre, follaje para ungulados silvestres y domesticados y reservas de semillas para mamíferos pequeños. En este estudio se examinan aspectos de la fenología, compatibilidad, biología de la polinización y características de la progenie de diversos lotes de la maleza amarga (Purshia tridentata) y de un híbrido putativo entre esta misma especie y Purshia stansburiana. Con la excepción de los tratamientos de polinización abierta y por viento, la polinización masiva se logró en la etapa de antesis dentro de bolsas de papel blanco, las cuales se usaron para aislar las ramas del tratamiento. Al parecer, la maleza amarga es mayormente auto-incompatible y necesita de algún agente, ya sea del viento o algún animal, para efectuar la polinización. Aunque la polinización de las flores de maleza amarga sin duda se lleva a cabo principalmente a través de insectos, es posible
