45-55 Million Year Old Orchid Pollinaria Attached to Pollinating Insect Found in Piece of Baltic Amber

A new study published in the Botanical Journal of the Linnean Society documents evidence of an orchid fossil trapped in Baltic amber that dates back 45-55 million years ago (Eocene epoch), beating the previous record for an orchid fossil found in Dominican amber some 20-30 million years old.

A fungus gnat trapped in Baltic amber some 45-55 million years ago is carrying on the upper portion of its severed leg a pollen sac from an orchid. Image credit: George Poinar, Jr.

Orchids have their pollen in small sac-like structures called pollinia, which are attached by supports to viscidia, or adhesive pads, that can stick to the various body parts of pollinating insects, including bees, beetles, flies and gnats. The entire pollination unit is known as a pollinarium.

In this study, a small female fungus gnat was carrying the pollinaria of an extinct species of orchid – named Succinanthera baltica — when it became trapped in amber more than 45 million years ago. The pollinaria was attached to the base of the gnat’s hind leg.

Amber preserves fossils so well that paleontologists could identify a droplet of congealed blood at the tip of the gnat’s leg, which had been broken off shortly before it was entombed in amber.

Succinanthera baltica shows that orchids were well-established in the Eocene epoch, and it is likely that lineages extended back into the Cretaceous period.

Until such forms are discovered, the specimen provides a minimum date that can be used in future studies determining the evolutionary history and phylogeny of the orchids.

How Succinanthera baltica’s pollen ended up attached to the fungus gnat and eventually entombed in amber from near the Baltic Sea in northern Europe is a matter of speculation.

“But orchids have evolved a surprisingly sophisticated system to draw in pollinating insects, which may have led to the gnat’s demise,” said lead author Prof. George Poinar, Jr., of Oregon State University.

“We probably shouldn’t say this about a plant, but orchids are very smart. They’ve developed ways to attract little flies and most of the rewards they offer are based on deception.”

Left: underside of anther cap and pollinarium of Succinanthera baltica in Baltic amber. H – congested haemolymph drop attached to the tip of severed hind leg; V – viscidia. White arrow shows area where pollen grains were photographed. Scale bar – 170 µm. Right: portion of pollinium with pollen grains of Succinanthera baltica. Scale bar – 60 µm. Insert shows magnified view of individual grains (arrow). Scale bar – 48 µm. Image credit: George Poinar, Jr. / Finn N. Rasmussen, doi: 10.1093/botlinnean/bow018.

Orchids use odor, color and the allure of nectar to draw in potential pollinating insects.

They will emit a scent that suggests to hungry insects the promise of food, but after entering the flower they will learn that the promise of nourishment was false.

Likewise, female gnats may pick up a mushroom-like odor from many orchids, which attracts them as a place to lay their eggs because the decaying fungal tissue is a source of future nutrition. Alas, again it is a ruse. In frustration, they may go ahead and lay their eggs, dooming their offspring to a likely death from a lack of food.

Finally, male insects are attracted by the ersatz scent of female flies and they actually will attempt to copulate with a part of the orchid they think is a potential mate.

“All three of these processes are based on deception and they all have the same end result,” Prof. Poinar said.

“Though the deception works in different ways, the bottom line is that the orchid is able to draw in pollinating insects, which unwittingly gather pollen that becomes attached to their legs and other body parts, and then pass it on to the next orchid flowers that lure them in. Orchids are, indeed, pretty smart.”

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George Poinar, Jr. Finn N. Rasmussen. 2017. Orchids from the past, with a new species in Baltic amber. Bot J Linn Soc 183 (3): 327-333; doi: 10.1093/botlinnean/bow018

This article is based on text provided by Oregon State University.