It is considered good practice in herbaria today to place just one collection on a sheet. This might include more than one plant, if they are small, but these are the result of one collection event, in one location. That wasn’t always the case in the past, and even today some curators, conscious of the high cost of herbarium sheets, hate to see a great deal of space go to waste. If the specimen is small, it might be positioned on a sheet so that there is room for at least one other specimen of the same species collected sometime in the future. But if the plant is very small the temptation may remain, and result in rather interesting sheets. At one point on Twitter, there seemed to be a contest to see who could come up with the most crowded sheet, with one entry from the Natural History Museum, London (NHM) a sheet with six specimens, followed by the Royal Botanic Garden, Edinburgh with eight fern specimens.
Then NHM countered with a nine-specimen example, where the barcodes seemed more obvious than most of the plants. They also upped the ante by noting that one of the specimens had been collected by the great British ecologist Charles Elton. Later, the Royal Botanic Garden, Kew entered the fray with another nine-specimen sheet, this time of orchids, made more crowded with lengthy accompanying notes. All these sheets were of flowering plant specimens. When it comes to mosses, at least in the past, such examples multiply, with several packets attached to a sheet. Now many curators favor envelopes or packets stored in boxes or drawers, and much work has been done, often in combination with digitization projects, to remove packets from sheets.
Sometimes it is not entire specimens that are pasted on sheets, but multiples of some plant part, often to show variation. On a visit to the Basel Herbarium, the visual artist Bea Eggli saw pages of orchid flowers and Tweeted that “I always find a piece of my identity in herbaria.” To me, this is rather cryptic, yet I can relate to it; the order and variation of form are intriguing (see image above). The flowers from several species of Serapias were preserved by the botanist Jany Renz in the 17th century to show variation within and among species. They were displayed by the Basel Herbarium during a 2022 conference to commemorate the 400th anniversary of the publication of Caspar Bauhin’s Flora of Basel.
A somewhat similar approach was taken more than 400 years later by Norman Douglas Simpson (1890-1974) with leaves of Hedera ivy species and cultivars. This reminds me of work done in the tradition of Johann Wolfgang von Goethe, with variations on a theme or type. They display just how much variation there can be even within a single specimen, let alone in genera, and also different kinds of variation from size to wide variations in shape; these leaves vary from entire to having from three to five lobes in various forms.
There is yet another play on the unity and variety theme. That’s when collectors amass a number of specimens from the same area at the same time. Most commonly, the aim is to provide duplicates, herbarium coinage, to be sent to other institutions as insurance against a future calamity, or in trade to build species or geographic diversity in a collection. But in a post from his lab, Mason Heberling, curator of botany at the Carnegie Museum of Natural History, Pittsburg, discussed five specimens of large-flowered trillium (Trillium grandiflorum). All of them remain in the herbarium because they are vouchers for a study the collectors, Frederick Utech and Mashashi Ohara, published along with Shoichi Kawano in 1984. Each sheet shows a different stage in the species’ life cycle, from small seedlings to large plants with flowers. Since this plant is a spring ephemeral, such a wide variety of stages is more likely to be found in one place. Heberling notes that Utech and Ohara were ecologists, not taxonomists, so they were more interested in life history. They found that many herbarium collections did not provide specimens that adequately documented different developmental stages. So their collections were an attempt to collect differently, and their article an argument for why others should do the same so ecologists would find more valuable material in herbaria and thus become more likely to use what could be an excellent research resource.
Heberling himself does ecological studies and has published a good review of why ecologists have tended to underutilize herbarium collections and what can be done to make them more useful to this community (Heberling, 2022). Documenting life history is one strategy and obviously not a new one. Also used in the past was something that botanist and corn expert Edgar Anderson and W.B. Turrell wrote about in 1935: mass collections. This involves supplementing specimens with large numbers of a particular plant part. One example would be collecting regular specimens from two or three maple trees at a site, and then gathering one leaf from each of 30-50 trees. In other cases, inflorescences or fruits might be saved. These could allow studies of the frequency of variations, any discontinuities in these variations, and also correlations between variations. In other words, multiples matter.
Anderson, E., & Turrill, W. B. (1935). Biometrical studies on herbarium material. Nature, 136 (3451), 986. https://doi.org/10.1038/136986a0
Heberling, J. M. (2022). Herbaria as big data sources of plant traits. International Journal of Plant Sciences, 183(2), 87–118. https://doi.org/10.1086/717623