US National Herbarium

I've been working with the Smithsonian's Natural History Museum in Washington, DC over the past week.  The museum maintains the US National Herbarium, spanning the top two floors of the building and houses around 5 million dried plant specimens.  Not many people have heard of it: the area is highly secure, climate controlled, and open only to researchers with permits.  So why has it existed since 1848?  In the history of people studying plants, herbaria were prime resources for documenting species discovered in unexplored parts of the world. Explorers would go out looking for plants, harvesting branches and flowers to be dried for storage in an herbarium.  These plant records could then be used as standards by which to determine new species or subspecies, again as all of this was done visually before our understanding of modern genetics.  This led to the careful preservation of plant samples for future study.  Most of these herbaria were commissioned by universities, botanic gardens, governments, or private individuals.

An R. viscosum herbarium specimen collected on June 6th, 1876 in Washington DC, the population has since been lost to urbanization. The branches do not press themselves: someone went in initially and folded the leaves, flowers over to mimic how the plant appeared when it was sampled in the wild.  It is very much an art.  The Smithsonian maintains a staff dedicated to going through the collections and conserving the specimens for future use.  

Herbarium specimens such as those at the National Herbarium are also used by researchers to extract DNA from plant tissue.  Such a study would be akin to populations genetics studies described here using historical specimens.  My purposes here were to look at blooming time from herbarium records of R. viscosum in the DC area.  Most of the 100 or so specimens I looked at were taken in full bloom, with blooming dates that varied year to year from 1876 until 2004.  I will look for correlations between monthly temperature averages in the DC area and how this affects the blooming time in this species, if at all.  This will help inform us about the variation I've observed across the country for flowering: it could be dependent on temperature in a given month, or not.  Historical records will help us to determine this.  From a practical standpoint, this knowledge will help us to determine how useful breeding for later or early blooming time could be.  If it is not strongly dependent on the weather in a given year, my field observation would support a genetic component to this trait based on the range of blooming times within populations that we could alter through directed breeding.  

R. viscosum flower. Each flower was positioned before applying pressure so that the dimensions and floral parts would be preserved.

Specimens are preserved in large file cabinets above the museum.

Despite the urbanization and suburbanization in this part of the country, I was able to locate some wild populations of R. viscosum in local parks. The plants were similar to those I found in Arkansas, and appeared to be early blooming as well as they all recently finished flowering as of this week.  The species is scattered along rivers, growing in sandy soil.   At about 1,000 miles from the populations sampled from Arkansas to Florida, these northeastern individuals will serve as an "oddball" in the population genetics analysis, as I would expect them to be genetically distinct from those in the southern US.  I'll see how the hypothesis holds up.  

Gone are the days of commutes down dirt roads

R. viscosum, Wolf Trap Park. Vienna, VA. Thank you Laura Hoffman for the collection help!