Canada frostweed (Helianthemum canadense(L.) Michx.; Cistaceae) at the northeastern limit of its range: implications for conservation

Abstract

Canada frostweed (Helianthemum canadense) is a perennial herb whose abundance and habitat are declining in Nova Scotia. These sites mark the northeastern limit of this species with nearest populations occurring in Maine and Quebec. To determine the genetic structure of northeastern populations, we used amplified fragment length polymorphisms to examine individuals from Nova Scotia, Maine, New Hampshire, and Quebec. Cluster analyses and analysis of molecular variance identified four groups: (i) Queens County, Nova Scotia; (ii) Kings County, Nova Scotia; (iii) Quebec; and (iv) Northeastern New England. New England samples revealed evidence of gene flow among populations within that region, and several individuals from Quebec and Queens County, Nova Scotia, were assigned to the same cluster. The majority of individuals from Kings County were assigned to a separate cluster from that associated with Queens County, indicating two distinct populations within Nova Scotia. Differences between Nova Scotia populations may be attributed to isolation and drift, or separate postglacial colonization events. We recommend that Queens County and Kings County populations be considered as discrete units for conservation and, because Nova Scotia populations are distinct from other populations in eastern Canada and northeastern United States, we suggest that conservation of populations at the northeastern limits of the range of H. canadense is warranted.