They may look like this shrub's own spring blossoms, but these dainty flowers reveal the presence of an invader. They belong to the parasitic plant Pilostyles thurberi, which has infested this shrub. Only the buds poke through the bark; the rest of the parasite hides within the branch, supping its host's nutrients.
More than 3900 species of plants—about 1% of the world's total—swipe their sustenance from other organisms, says botanist Daniel Nickrent of Southern Illinois University, Carbondale. His Parasitic Plant Connection, launched 5 years ago, is a clearinghouse of information on these botanical thieves, including mistletoes, sandalwood, morning glories, and the world's largest flowers—the Rafflesiaceae of Indonesia, which grow up to a meter across and reek like rotting flesh. The site provides distribution maps and key characteristics for 18 families of parasitic plants. There's also a directory of researchers, an update on phylogeny, a glossary, and links to scores of images and to gene sequences. Despite their life-sapping reputation, Nickrent notes that most parasitic plants take only a small fraction of their host's resources—much less than a lawyer's 33%, for instance.