Near the top of the hike up Signal Hill where Antigua’s last remaining rainforest gives way to rocky barrens, clumps of a long and deceptively pretty plant with a bright, citrus aroma sprout from the volcanic soil. It’s lemongrass — that ingredient we all love in Thai curries and soups, but an invasive species that grows fast and burns easily on this Caribbean island because of the high oil content in its leaves.