From Field to Herbarium, Documenting Plant Diversity
Daniel Atha is an Associate Editor of NYBG‘s systemic botany journal, Brittonia, and a researcher specializing in floristics, taxonomy, and economic botany. He has taught classes in anatomy and systemics at the Garden’s School of Professional Horticulture and is currently working on a project to develop identifying DNA barcodes for plants of the Northeastern United States.
Everything we know about every plant on earth can be traced back to a single preserved specimen stored in a herbarium. In service to mankind, the botanists of the world maintain a system of naming plants and sorting out how they are related and how to tell one from the other. Each species is authenticated by one and only one physical specimen that serves to define the species and provide a permanent and tangible record of its existence.
Herbarium specimens are available to plant breeders, chemists, foresters, researchers, government officials, and botany students around the world. You can go to–or borrow from–a herbarium just like you would a research library. The larger herbaria, like the NYBG’s own William and Lynda Steere Herbarium, contain millions of specimens–each one systematically filed in specially-designed cabinets stored in climate-controlled facilities assembled and maintained for the advancement of science.
How do the specimens get into a herbarium? Little has changed over the course of 250 years of plant exploration; each specimen begins with a plant collector going into the field, garden, or greenhouse and selecting a representative specimen. Each specimen includes a clipping of the plant with leaves and hopefully flowers and fruits. The inclusion of the flower and fruit in a specimen is very helpful because they can help to distinguish between closely related species. The collector notes details of the plant that are key to identifying it, like height, diameter, morphological characteristics, and odors and colors that will fade in the process of drying. The collector also records the exact location, habitat, date, and their name. The collector assigns a unique number to each specimen. The number will be used from then on to unambiguously and efficiently refer to that specimen.
Each specimen is then placed under pressure between two boards and dried over artificial heat. The heat drives off the water in the form of vapor and the pressure prevents wrinkling, maintaining the size and shape of the specimen. After it’s dried, the specimen is labeled, mounted, and filed in the collection. For a fascinating and well-written behind-the-scenes look into the herbarium collection, this post by Lisa Vargues provides a thorough introduction.
Two recent developments have added to the work of a plant collector, without changing the basic process. One is the advent of GPS; botanists now routinely carry a GPS device or smartphone allowing them to make an exact record of each plant’s location. Second, most collectors now also take a leaf sample for DNA analysis. The sample is placed into a small bag of silica gel that flash dries the tissue and preserves the DNA for later analysis. The DNA sample is labeled with the same information as the specimen, but is stored separately, often in a separate DNA bank such as the one at The New York Botanical Garden.
All the work of naming, sorting, and describing each new plant species is done directly from a stack of preserved specimens, representing the range of form, distribution, and habitat preferences of a given species. Herbarium specimens allow researchers and businesses to derive thousands of useful products from corn and soy, pinpoint the unique properties of wood, track global biodiversity, and ensure that countless beneficial plant-based products are, in fact, produced from the plants they are supposed to be derived from, like chamomile, coffee, and cat-nip. The herbarium specimens and their accompanying genetic data allow researchers to ensure that products and plants are exactly what they are supposed to be.