Conifers tower across the frigid swaths of land that span North America, northern Europe and Russia in a great ring around the world. Nestled within the photosynthetic tissue of the boreal trees – and within the bountiful cloud-like lichens and mosses that carpet the ground between them – are fungi. These fungi are endophytes, meaning they live within plants, often in a mutually beneficial arrangement. …Older studies have examined the correlation between biodiversity and latitude, which is often used as a proxy for climate. …it’s not that simple when it comes to fungi in the boreal zone. …Betsy Arnold, a professor in the School of Plant Sciences  thinks that the special climate dependence of these fungal endophytes reflects a process of co-evolution with their hosts – or “research and development,” as she put it – as plants find the ideal endophyte partner and flourish despite the distinctive stresses that plants face in these harsh northern landscapes.