Small, isolated populations are prone to genetic drift and high levels of inbreeding that can threaten their long-term survival. Alnus maritima persists exclusively in three groups of small, highly disjunct, regional populations in the Delmarva Peninsula, Georgia, and Oklahoma. Trees in the three regions are recognized as separate subspecies. Microsatellite markers were used to measure fine-scale population genetic diversity and structure (1) within and among regions and (2) within and among populations in each region. Compared to a previous study utilizing allozymes, microsatellite data show higher levels of variation, lower levels of inbreeding, but similar levels of genetic differentiation among regions. Significant genetic differentiation was detected among regions and among distinct populations within regions. Genetic differentiation was significantly correlated with geographic distance among regional populations, but not among populations within regions. Populations, therefore, likely represent fragments of formerly extensive networks of populations that have decayed and retracted due to competition with other species better adapted to the shadier habitats of late-succession environments. The unique genetic features of populations within different regions should be considered as part of future conservation efforts.

We isolated and characterized 19 microsatellite loci from the endangered seaside alder, Alnus maritima. Loci were screened in 24 individuals of A. maritima and four individuals of its congener the hazel alder, A. serrulata. The number of alleles per locus ranged from 2 to 6, observed heterozygosity ranged from 0 to 0.952, and the probability of identity values ranged from 0.126 to 0.850. These new loci provide tools for characterizing the population genetics of this rare tree.

The genus Drosera (sundews) is represented in British Columbia (BC), Canada, by Drosera rotundifolia (L.), Drosera anglica (Huds.), and their hybrid Drosera × obovata (Mert. & W.D.J. Koch). All three can be found in Sphagnum bogs of central BC, including those within the Aleza Lake Research Forest (ALRF) located 60 km east of Prince George. Vegetation patterns in bogs are known to be correlated with light, water, and nutrient gradients, and despite information being available on the influence of light and water on Drosera occurrence, little information is known about the role of nutrients. Here, we focused on a bog containing all three Drosera species, to determine whether nutrient levels are related to the abundance of the widespread species, D. rotundifolia. Univariate regression tree analysis between soil water chemistry and D. rotundifolia numbers indicates that D. rotundifolia is a calcifuge, preferring moderately acidic soil pH (>5.5) and relatively low calcium levels (<2.88 ppm). This study provides evidence that high soil water calcium and low pH limit the growth of D. rotundifolia in field populations. The physiology underlying this preference, how this is affected by hybridization between other sundew species, and how this mineralogical limitation interacts with other niche-defining factors to dictate the occurrence of D. rotundifolia are questions that remain to be answered.

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