The ecology and distribution of the Genus Circaea (L.) in Nova Scotia

The ecological and distributional relationships between the sterile interspecific hybrid, Circaea X intermedia, and its parent species, C. alpina and C. quadrisulcata var. canadensis, are investigated. Using information from herbarium records, and evidence based on habitat vegetation, associated species, and several chemical and physical soil properties, it is concluded that the three taxa are ecologically distinct. Furthermore, it is shown that they are differentially correlated with erosional and depositional features resulting from the evolution of a river system. The impact of human related disturbance on the population dynamics of C. quadrisulcata var. canadensis and C. X intermedia, and their abilities to tolerate disturbed conditions, are discussed. It is suggested that disturbance pressure has resulted in an increase in C. X intermedia populations while C. quadrisulcata var. canadensis populations have decreased. If disturbance pressure continues to affect these taxa, it is predicted that these trends will continue and thus place the future of C. quadrisulcata var. canadensis in jeopardy. The geographical distributions of the three taxa are presented. Emphasis is placed on the distribution of C. quadrisulcata var. canadensis which shows a discontinuity in its range by being confined entirely to northern Nova Scotia. The cause of this discontinuity is attributed to differences in bedrock geology between northern and southern Nova Scotia although differences in precipitation patterns between these two areas cannot be ruled out as a possible factor as well. A similar correlation between the northern boundary of C. quadrisulcata var. canadensis and the Canadian Shield-sedimentary rock contact across eastern and central North America is pointed out. The similarity of these rocks to those in Nova Scotia and the corresponding distribution patterns of C. quadrisulcata var. canadensis suggest that bedrock type is the main factor influencing the distribution of C. quadrisulcata var. canadensis in Nova Scotia. In general, the range of C. X intermedia is found to correspond well with the area of range overlap of C. alpina and C. quadrisulcata var. canadensis. However, a few populations occur allopatrically to C. quadrisulcata var. canadensis in southern Nova Scotia. The significance of these allopatric populations in relation to the restriction of C. quadrisulcata var. canadensis to northern Nova Scotia is discussed. It is concluded that they probably reached their present locations in southern Nova Scotia as a result of hybrid diaspore dispersal through the operation of normal dispersing mechanisms.