While taxonomists are still heavy users of herbaria, there are more and more ecologists and environmentalists using collections to document environmental changes such as global warming, species extinctions, and ecosystem degradation. This is one reason why georeferencing of label data has become crucial. It is important to know not only when a specimen was collected for studies in phenology, but also precisely where it came from. Georeferencing essentially means identifying the latitudinal and longitudinal coordinates of a location, and estimating the probability of the collection within a certain radius of that point. The more accurately the location can be determined, the smaller the radius. There are now programs such as Geolocate that aid in determining the radii, but it is still a time-consuming process that explains why most recent collections report GPS coordinates. Other collection practices have also changed, with small pieces of living material often being packed in drying gel for future DNA sequencing. Dried specimens can be used, but fresh material is much easier to work with and provides more detailed results. However, DNA analysis is one of the unanticipated uses of older specimens as well. Analysis techniques have improved greatly over the past 10 years which means that more and more specimens that are 100 or even 200 years are yielding sequence information. This is a real boon for phylogenetics, evolutionary ecology, and also for pharmaceutical exploration. Since so many drug compounds were originally found in plants, the medicinal study of plants has seen a resurgence of an interest that was significant during the Renaissance.
This use of historical material brings up another issue. Many specimens from the 19th century are darkened. They simply look dirty, but the darkness is due to treatment with mercuric chloride to prevent insect damage. This destroys the DNA in the specimens but is also a risk for those handling the plants. Dealing with this problem is one of the ways that specimen preparation and handling have changed the most over the years. While mercuric chloride hasn’t been employed for decades, it’s presence is still felt in herbaria with historical material. Curators and herbarium managers are always on the lookout for ways to minimize staff exposure and to decontaminate cabinets and storage areas. However, these specimens are too valuable to discard, particularly now when they have been in a sense rediscovered as time capsules of historical ecological information.
Today, many herbaria control insects primarily by freezing specimens at -20° for seven days or more both when they enter the herbarium and again before they are placed in cabinets. Insect traps are used in monitoring, but usually chemical treatment isn’t necessary, especially if the cabinets are well-sealed. Some smaller herbaria still rely on camphor balls in each cabinet. This doesn’t help air quality, but is effective and much less dangerous than mercury. Bringing up this topic may seem like an aside in a discussion of labeling, but there are herbaria where old specimens are stamped as having been treated with mercuric chloride to warn handlers of the danger.
I would like to end with a reminder that no matter the amount or quality of the information on a herbarium label, there is always a great deal left unsaid, a rich tapestry that underlies every specimen. The great plant collector Frank Kingdon Ward (2003) writes in his book, In the Land of Blue Poppies, about a case where he had seen a promising rhododendron. When he returned to the site: “The flowering specimen of the rhododendron I had worked so hard to get [in a remote mountainous area] had set no seed. One truss of two flowers I had taken lightheartedly for the herbarium. The other two trusses, four flowers in all, hadn’t produced a seed. I nearly wept. And then as I was on the point of giving up, hidden away in a crevice of the cliff I found one more plant. It had one capsule, and it was full of fertile seed. It had become a point of honor to collect seed of the pink rhododendron. Had it been a diamond as big and blue as the Koh-i-noor, I couldn’t have taken more care of it. May it succeed! Yet, when the plant flowers in England, connoisseurs looking at it and reading the simple label, ‘Rhododendron sp. (K.W. 9413) Burma 1931,’ will think of none of these things” (p. 138).
My next series of posts describe efforts to deal with just this issue of linking the excitement of collecting with the rich scientific and historical data in herbarium sheets.