A common ornamental tree planted along sidewalks and in gardens throughout the world, Ginkgo biloba–also called the maidenhair tree–has been considered a source of herbal medicine for millennia. During the 1990s, several studies showed the extracts helped improve memory in patients with dementia (ScienceNOW, 30 May). And today, ginkgo is a popular remedy sold not just for memory loss but also for ailments ranging from depression to hemorrhoids.
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further investigation indicated that live ginkgo cells were harboring algal “ghosts”: nondescript cell bodies that lacked a nucleus or chloroplast. When ginkgo cells died, these ghosts came back to life, transforming themselves into free-living, photosynthesizing algae.
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In living cells, the algae depend on the ginkgo for food. In return, it’s possible that the algae somehow help produce the ginkgo’s medicinal compounds, he suggests. Not much is known about the synthesis of these unique compounds except that making them requires two compartments–the cytosol–and “some unknown organelle,” says Huss. That organelle might be the algae.

Whatever the nature of the partnership, it could be more than a hundred million years old. Ginkgos date back to the dinosaurs, and researchers know already that the two other plants dating back that far back depend on symbiosis to survive. “That makes me think that symbiosis is part of an ancient story,”