WHAT IS AN HERBARIUM, AND WHAT IS IT GOOD FOR? By Lyn Loveless
An herbarium is an archive of dried, pressed plant specimens mounted on archival paper. These herbarium sheets, the label information they contain, and the people who know and manage these collections are essential resources for research, teaching, public outreach, and environmental management. They provide the basis for virtually all our historical knowledge about plant diversity, systematics, distribution, and adaptation. Each herbarium specimen consists of a pressed plant, with its associated collection data, and each specimen creates a physical record that documents that plant’s presence and appearance at a given time and place. Herbarium archives help us to identify newly collected plants, describe and name new species, map changes in plant distribution, compile floristic data, and track evolutionary changes in plant lineages. These data are essential not only to systematic botanists, who seek to catalogue plant diversity and understand evolutionary relationships among plant groups, but to teachers, ecologists, agronomists, resource managers, medical professionals, climatologists, evolutionary biologists, chemists, paleobiologists, anthropologists, ethnobotanists, conservation biologists, and many other professionals who need to identify, locate, or understand plants on the landscape.
Herbarium holdings are rich and irreplaceable records of the natural history of our planet. They literally connect the past with the future. They are a vast library in which we can read biological, environmental, and evolutionary history. The unique value of these archives is that they provide a series of snapshots of plant diversity over time. They document shifts in species distribution and abundance that may have resulted from land use changes, environmental fluctuations, or competition with invasive or expanding species. Older collections are a priceless legacy of plant communities in habitats that are now often profoundly changed or even extinguished. Other samples might document the spread of species to new locations or the gradual changes in stomatal density within in a population adapting to a changed environment. Herbaria and other natural history collections are, almost by definition, long-term datasets, “big data,” historical records that can inform our decision-making in the environments of the future.
Although herbarium specimens are inherently physical, most herbaria have now digitized their collections, making high-resolution scans or photographs accessible to online users. Students can examine specimens in herbaria across the globe to answer a myriad of questions. A researcher can compare collections of the same species from different locations to describe the variation present in a lineage. A flowering collection gives us data on reproductive seasonality. Insect damage on leaves or fruits provides an historical record of herbivory. Some specimens have insect eggs or fungal pathogens hitchhiking on their leaves, revealing important plant-animal interactions. But images have their limits. The actual plant specimens must also be conserved, if they are to be used for genetic, chemical, or microscopic observation. Plant tissue can be sampled for chemical analysis, and in some cases, seeds from dried specimens can even be germinated to produce a living (but very old) plant. Dried plant specimens also retain their DNA intact. Researchers can sample leaves from this deep historical record to compare DNA genetic markers in a given species over time.
In the past three decades, molecular phylogenies based on DNA similarities (many of them analyzed from herbarium specimens) have completely rewritten our understanding of the relationships between plant groups. The priceless materials held in herbarium specimens make it easy for geneticists to compare DNA sequences between different species, even species that are now extinct in the wild. Who can say what future technological developments will also depend on the contents of modern herbaria? It is incumbent on institutions of learning to exercise the foresight and vision to appreciate, to sustain, and to enable the future development of these unique and irreplaceable collections.
In colloquial language, an “herb” is a savory or aromatic plant that is used to season food. But an herb can also mean “a plant,” and an herbarium is a library of samples of plants and plant-like organisms (often including algae, mosses, lichens, and fungi).