Age-Old Orchid

15-20 million year old stingless bee preserved in amber. The stuff on its back are pollinia--and represent the only known piece of fossilized orchid ever discovered. Photo credit: Santiago Ramírez.

Friday, August 31st, 2007--

A recently discovered piece of amber contains the first confirmed orchid fossil ever found. The ancient orchid, classified as Meliorchis caribea, reveals new information about the origin of orchids. "The question is: how old are they?" asks Santiago Ramírez, of the the department of organismic and evolutionary biology and the Museum of Comparative Zoology at Harvard University in Cambridge, MA. "There's been a lot of speculation."

Orchids are unlikely to become identifiable fossils for several reasons: they have nondescript leaves, their pollen doesn't blow in the wind so it doesn't get trapped in sedimentary lakes where many plant fossils form (they rely solely on insects and birds to carry pollen) and they live in small populations.

Because of the absence of orchids in the fossil record, estimates of the age of the orchid family vary widely. The prevailing thought was that orchids emerged relatively recently, probably sometime after the dinosaurs went extinct 65 million years ago. "Orchids require specific insect pollinators. So this led people to think that they must be very young," says Ramírez. The thinking was that orchids would have had to appear later than the specialized pollinators they rely on. LISTEN TO RAMÍREZ>>(mp3)

But in 2001, DNA studies linked the orchid family to the ancient Asparagales order (of which asparagus is a member), suggesting that the orchid family, which contains somewhere between 20,000 and 30,000 species, is older than previously thought. LISTEN TO RAMÍREZ>>(mp3)

With the 15- to 20-million-year-old piece of fossilized amber in hand, Ramírez and his colleagues may have solved the age-old mystery. The fossil, dug out of a mine in the Dominican Republic in 2000 by a private amber collector, contains orchid pollinia--a clump of pollen--attached to the torso of a now-extinct stingless bee (Proplebeia dominicana). LISTEN TO RAMÍREZ >>(mp3)

The pollinia were clearly from an orchid, Ramírez says: "Only one other family produces pollinia but the pollinia is extremely different." From the pollinia's shape and its placement on the bee's body, the researchers deduced characteristics about the fossil's flower and were able to place it within the current orchid family tree. LISTEN TO RAMÍREZ>>(mp3)

This means that the branch of the orchid family tree where the fossil fits is least 15- to 20-million-years-old. By comparing the DNA of current orchids on this branch with other modern day orchids, the researchers arrive at an estimation for the age of the other branches on the tree. This is called a molecular clock analysis. LISTEN TO RAMÍREZ>>(mp3)

The researchers place the arrival of orchids between 76 to 84 million years ago. Ramírez and his colleagues published the findings in the journal Nature this week. Based on the study, Ramírez says, orchids coexisted with dinosaurs and likely started to flourish shortly after the mass extinction between the Cretaceous and Tertiary.

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--Flora Lichtman