Smithsonian Insider – Research collection of pollen grains given to Smithsonian Tropical Research Institute

Any child can recognize the difference between a rosebush and an oak tree, but given a sample of the tiny pollen grains produced by each of these two plants, few people could match the pollen with its owner. At a microscopic level, however, pollen grains are quite distinct in size, shape and surface structure.

Photo: This electron microscope image shows a pollen grain from the Asteraceae family of flowering plants.

The Smithsonian Tropical Research Institute in Panama was recently given a collection of more than 25,000 different pollen grains and spores, each mounted on a microscope slide and labeled according to the plant that produced it. “The collection is worldwide in coverage with an emphasis on plants of the Americas,” explains collection donor Alan Graham, professor emeritus at Kent State University and curator at the Missouri Botanical Garden.

Graham began the collection in 1954, gathering pollen from plants in the field and from dried specimens in large herbarium collections. A card catalog accompanying the collection is cross-referenced to the slides and contains information on each plant species represented.

Photo: Carlos Jaramillo uses a microscope to study pollen from the Graham collection. (Photo by Marcos Guerra)

Covered by a tough wall, or ‘exine,’ many pollen grains are incredibly resilient, so much so that they show up as fossils in sedimentary rock tens of millions of years old. “It is not unusual to find rich assemblages of fossil pollen and spores in sediments where no other plant fossils—leaves, stems, seeds—exist,” Graham says. Graham, a paleobotanist, uses fossil pollen to reconstruct the vegetative and ecological history of the Americas, with an emphasis on the last 100 million years. “To quickly identify the prehistoric pollen I retrieve from rocks, it was necessary to create this reference collection of known pollen types,” he explains. Some fossil pollen in the collection is 40 to 45 million years old.

A critical bit of information included in the plant descriptions in Graham’s card catalog are the ecological conditions under which each plant grows and its geologic range. This data is essential to understanding the history of the vegetation and environments of the New World, “giving us a picture of how the earth got to this one brief instant of time we are living in right now, and where it may be headed,” Graham says.

Carlos Jaramillo with labeled boxes that hold some 25,000 samples of pollen grains that were mounted on microscope slides by Alan Graham. (Photo by Marcos Guerra)

“This is one of the largest pollen collections in the world, unique in its coverage of North America and Latin America,” says Carlos Jaramillo, a stratigrapher at the Smithsonian Tropical Research Institute. “Soon, we plan to have all of the components of this collection in digital format, to share on the Web with everyone around the world.”