The ghost in the tree
In the dense Atlantic Forest, a plant exists in a way that challenges the definition of a plant. Apodanthes caseariae is an extreme parasite, a holoparasite, meaning it derives all of its nutrients from a host. It has no leaves, no stem, and no roots of its own. For most of its life, it is invisible, living as a network of fungus-like filaments or even individual cells inside the branches and stems of its host trees. This internal, vegetative body is called an endophyte. Histological studies show these parasitic cells positioned to draw nutrients directly from the host's vascular tissues.
This organism belongs to the family Apodanthaceae, a small group of endoparasites found worldwide. Genetic analysis has placed this family within the order Cucurbitales, which also includes cucumbers and melons. Apodanthes caseariae is specialized, primarily infecting trees of the genus Casearia (family Salicaceae). The relationship is completely one-sided; the parasite is so effective that it can prevent the host tree's branches from flowering. The plant's own body is so reduced that its chloroplast genome—the set of genes for photosynthesis—is a tiny, non-functional relic of its evolution.