HAWTHORNS (CRATAEGUS: ROSACEAE) OF THE CYPRESS HILLS, ALBERTA AND SASKATCHEWAN

This paper describes the ecological situation of Crataegus found in the Cypress Hills of Alberta and Saskatchewan in the context of climate and vegetation patterns, followed by a detailed account of the taxa present. Crataegus species are shown to be extremely numerous in certain habitats and are by far the most abundant shrubby plant of the Cypress Hills. A peculiar combination of physical factors of relief, temperature, precipitation and soil have given rise to a remarkable ecological island. Thirteen species of Crataegus are shown to occur compared with three in earlier work. Seven of the species, C. cupressocollina, C. aquacervensis, C. rivuloadamensis, C. purpurella, C. rivulopugnensis, C. rubribracteolata and C. ursopedensis are new to science and most of them are at least locally common in the Cypress Hills. In addition, C. sheridana A. Nels. has been resurrected. Also one new variety, saskatchewanensis, of C. sheila-phippsiae is described. Four of the new taxa appear to be restricted to the Cypress Hills although more intensive fieldwork in Montana might alter this. The biogeography is discussed in the context of Great Plains Holocene vegetation change and the small amount of information available on their differential ecology. All taxa are keyed and the new taxa are each fully described and illustrated. This work is based on over 500 collections, over 450 of which are by the authors. En este artículo se describe la situación ecológica de Crataegus en los Cypress Hills de Alberta y Saskatchewan en el contexto de patrones de clima y vegetación, seguido de un informe detallado de los taxa presentes. Las especies de Crataegus son extremadamente numerosas en ciertos hábitats y son con mucho las plantas arbustivas más abundantes de las Cypress Hills. Una combinación peculiar de factores físicos de relieve, temperatura, precipitación y suelo han dado lugar a una isla ecológica singular. Se demuestra la presencia de trece especies de Crataegus comparadas con las tres de un trabajo previo. Siete de las especies, C. cupressocollina, C. aquacervensis, C. rivuloadamensis, C. purpurella, C. rivulopugnensis, C. rubribracteolata y C. ursopedensis son nuevas para la ciencia y la mayoría de ellas son al menos localmente comunes en las Cypress Hills. Además, sheridana A. Neis, ha sido resucitada. También se describe una nueva variedad, saskatchewanensis, de C. sheila-phippsiae. Cuatro de los nuevos taxa parecen restringirse a las Cypress Hills aunque un trabajo de