While on a hike with my kids, we discovered a light, springy green plant growing in small clumps on the trail. According to a signpost, the plant is commonly called deer moss, but it’s not actually a moss at all. It’s a lichen. A lichen is a fungus and an alga growing together in a mutualistic relationship in which both organisms benefit from each other. Neither the fungus nor the alga can survive on its own, but together they form a hardy plant that can live in some alpine areas for up to 4,500 years. Because the plant can withstand…