These red maple (Acer rubrum) leaves were collected by Dorothy Pearth on November 6, 1959 at Coles Summit in Huntingdon county, Pennsylvania. Dorothy Pearth (1914-1996) was a curator at the Carnegie Museum. She made two special notes on the label: “with exceptionally long petioles” and “many leaves with very long petioles.” (Petioles are the stalks that connects leaf to stem.)
Herbarium data are often considered “biased.” All data collected haphazardly or by many different people across centuries with different intended purposes undoubtedly skew reality to some extent, depending on the research question. It is rightfully something to consider when using specimens in research. Taxonomic bias (what species are collected), geographic bias (where specimens are collected – more often near roads, for example), temporal bias (high collection effort in some years), or collector bias (“that guy never collects grasses”) are just a few to consider. But just because “bias” may exist doesn’t mean it can’t be accounted for or the data are somehow useless. Far from it!
In fact, “bias” can be a great thing! We want those “odd” specimens (like this red maple) documented because they often tell us something important. Maybe that specimen flowering in fall that normally flowers in summer is a sign of climate change. Maybe that unfamiliar species is the first record of an introduced species that will likely become invasive in the region. Maybe that specimen that resembles species X, but has really huge leaves, is a new species! Many undetermined specimens (that is, those that are identified to species) are collected for that very reason. Many new species are first realized after someone points out that this specimen is “weird.”
A recent paper in the American Journal of Botany (Pearson & Mast, 2019) surveyed collectors and search specimen records that include “outlier terms” – in other words, additional notes on the label written by the collector to point out something unusual about the specimen. They found that this practice of pointing out outliers is an important route to detect early changes in the Anthropocene (the age of humanity). Unusual specimens are important sentinels, bringing our attention to critical biological changes that may otherwise be overlooked in an era of rapid biological change.
Find this long-petioled red maple specimen online here: midatlanticherbaria.org/portal/collections/individual/index.php?occid=12233287&clid=0
Check back for more! Botanists at the Carnegie Museum of Natural History share digital specimens from the herbarium on dates they were collected. They are in the midst of a three-year project to digitize nearly 190,000 plant specimens collected in the region, making images and other data publicly available online. This effort is part of the Mid-Atlantic Megalopolis Project (mamdigitization.org), a network of thirteen herbaria spanning the densely populated urban corridor from Washington, D.C. to New York City to achieve a greater understanding of our urban areas, including the unique industrial and environmental history of the greater Pittsburgh region. This project is made possible by the National Science Foundation under grant no. 1801022.
Mason Heberling is Assistant Curator of Botany at the Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.