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Mycorrhizal associations are plant-fungal mutualisms that are fairly ubiquitous and likely evolved multiple times in phylogenic history; however, some plant families have consistently been identified as non-mycorrhizal, including the Brassicaceae. In this paper, we reviewed the literature and DNA databases for potential mechanisms that preclude mycorrhizal symbioses in the Brassicaceae and for exceptions to the general observation of non-mycorrhizal status within this plant family. In instances of association between members of the Brassicaceae and arbuscular mycorrhizal fungi we posed hypotheses for why these interactions occur in the species and sites observed. Instances of inconsistent association with mycorrhizal fungi were attributed to inter- and intraspecific variations in plant biology, disagreements in vernacular, methodology contradicting historical mycorrhizal surveys, and association being a facultative, variable trait that is determined by species-site interactions. We propose further research on a) the extent of mycorrhizal association in the Brassicaceae, b) the molecular mechanisms dictating association, and c) whether Brassicaceae-mycorrhizal fungal interactions result in nutrient transfer, and their particular roles in the family’s distribution across heterogeneous and harsh environments. 

PremiseThe success or failure of propagules in contrasting microhabitats may play a role in biological invasion. We tested for variation in demographic performance and phenotypic trait expression during invasion byAlliaria petiolatain different microhabitats. MethodsWe performed a reciprocal transplant experiment withAlliaria petiolatafrom edge, intermediate, and forest understory microhabitats to determine the roles of the environment and maternal source on traits, fecundity, population growth rates (λ), and selection. ResultsObservations ofin situpopulations show that edge populations had the highest density and reproductive output, and forest populations had the lowest. In experimental populations, population growth rates and reproductive output were highest in the edge, and the intermediate habitat had the lowest germination and juvenile survival. Traits exhibited phenotypic plasticity in response to microhabitat, but that plasticity was not adaptive. There were few effects of maternal source location on fitness components or traits. ConclusionsAlliaria petiolataappears to be viable, or nearly so, in all three microhabitat types, with edge populations likely providing seed to the other microhabitats. The intermediate microhabitat may filter propagules at the seed stage, but discrepancies betweenin situobservations and experimental transplants preclude clear conclusions about the role of each microhabitat in niche expansion. However, edge microhabitats show the highest seed output in both analyses, suggesting that managing edge habitats might reduce spread to the forest understory.