Le Phragmites australis au Québec: distribution géographique, nombres chromosomiques et reproduction

Abstract

A study of Phragmites australis (Cav.) Trin. ex Steud., the common reed, was conducted in Quebec between 1985 and 1991. Its present and former geographical distributions (before and after 1950) were established, the chromosome numbers of 52 individuals were determined, and various observations on the reproduction of this species by seed were made. The geographical distribution was outlined after consultation of 21 north-eastern american herbaria and upon in situ observations along roadsides in most parts of inhabited Québec. Concurrently, 77 representative populations were selected and visited in the summer and fall of 1985, allowing the observation of the degree of flower development, the frequency of seed setting, and the presence of smut, Claviceps microcephala (Wallr.) Tul. The chromosome numbers show a high degree of aneuploidy and vary between 2n = 42 and 59. The nordic populations tend to have a lower chromosome number and a faster flower development. In fact, for a given geographical area and date of collection, the flowers of the individuals with higher chromosome numbers are usually less developed. There is however a persistent problem with the evaluation of the chromosome number of a stand because of internal variations. Seed production is generally very low, but some stations, even nordic, are quite productive (up to 59.2% of flowers with seeds). The seeds are able to germinate under laboratory conditions, but it is not known yet if the plant can reproduce in this manner in the field. The seedlings develop slowly and seem to have poor competitiveness. Key words: Phragmites australis, distribution, chromosome numbers, reproduction, Quebec, weed.