Scanning electron microscope (SEM) photograph of a diatom on a lodgepole pine needle from Upper Geyser Basin, Yellowstone National Park

Scanning electron microscope (SEM) photograph of a diatom on a lodgepole pine needle from Upper Geyser Basin. A 10 micrometer (µm) scale is shown at the bottom of the image (slightly less than the width of human hair). Diatoms are eukaryotic unicellular algae that have silica (opal) skeletons and are ubiquitous in both freshwater and marine environments and can live in both acidic and alkaline environments. Image taken in October 2023 by David Damby (USGS). The needle was collected under Research Permit YELL-SCI-8030.