An invisible existence
Deep within the seasonally dry tropical forests of Morelos, an entire plant lives a life unseen. Bdallophytum americanum is a holoparasite, meaning it derives all of its water and nutrients from a host plant, completely abandoning photosynthesis. It has no leaves, no stem, and no true roots of its own. Its entire vegetative body exists as a network of filamentous threads, much like a fungal mycelium, that penetrates and spreads throughout the roots of its host. This internal system is known as an endophyte. For most of its life, B. americanum is completely invisible, its presence known only to the host trees, which are typically members of the genus Bursera—the same family as frankincense and myrrh.
The parasite's threads tap directly into the host's vascular system, primarily the phloem and secondary xylem, to siphon off the products of photosynthesis. This extreme adaptation to a parasitic lifestyle is so effective that the plant has shed all the typical features that would identify it as a flowering plant. For many years, its classification was uncertain. Botanists historically placed it and its relatives in the family Rafflesiaceae, alongside other bizarre, non-photosynthetic parasites like the famous corpse flower. This grouping was based on their shared, highly-reduced physical forms, a result of convergent evolution.
A surprising family tree
The only time Bdallophytum americanum reveals itself is when it reproduces. From the shallow roots of the host tree, fleshy, fungus-like inflorescences erupt directly from the soil. These structures, typically 8 to 15 centimeters tall, are a striking cherry-red to purple color and bear small, scale-like leaves. The species is dioecious, meaning individual plants produce either male or female flowers. Male flowers have bright yellow, conspicuous appendages on their stamens, while female flowers have a prominent yellow stigma, both of which serve to attract pollinators like hoverflies and carrion flies.
It was the advent of molecular phylogenetics that finally solved the puzzle of its ancestry. DNA analysis of its nuclear and mitochondrial genes revealed that B. americanum and its family, Cytinaceae, are not related to Rafflesiaceae at all. Instead, their closest relatives are in the order Malvales. This strange, subterranean parasite shares a common ancestor with familiar plants like cotton, hibiscus, and okra. This discovery demonstrated how an parasitic lifestyle can alter a plant's morphology, erasing millions of years of evolutionary history from its physical appearance and and its identity hidden within its genetic code.