Compiled by chairperson Jacquie Ashton
We were very lucky to have one of our assessors – Chris Bisson – giving the presentation at our AGM in 2023. Chris assesses the botanical accuracy of paintings being submitted into the archive, and he came to talk about herbaria as this is something we are developing in the Flori at the moment, so that in future there is an herbarium specimen of almost every plant painted for the archive. Listening to Chris and writing this article was both an interesting and educational exercise for me. I needed to research the people he referred to and looked at the links he gave for online websites and documents; some are updated (all the links are below), and it was fascinating to find out more about the history of herbaria and who was involved. He gave us so much useful information and I have tried to include as much as I can. I also added a new book to my collection. Now I am preparing my first specimens for the Flori herbarium and feel a lot more confident about doing it right.
More…: AGM presentation on herbaria given by Chris BissonYou can find very useful Herbaria References at the end of this article.
Chris Bisson’s background
Chris is currently the program Manager for the Foundation Degree in Horticulture based at the Eden Project University Centre. His degree was in Plant Sciences at Plymouth University, and after he was involved in ‘people and plants’ projects in Bristol, before working with Kew Gardens, alongside the Millennium Seed Bank project as an herbarium specimen digitiser and botanical literature researcher. With organisations overseas he was part of a team that put together species targeting guides. This required an understanding of phenology, to know the best time to collect plant specimens and seeds. His experience with herbaria goes back to 2003, as most of the information for the species targeting guides came from herbarium material. They provided a huge collection of historical information that provided the data he needed.
Chris explained that he gives ethnobotany students an assessed herbarium assignment where they collect and prepare 10 herbarium specimens and each plant needs to have an ethnobotanical use and he had brought some examples from last year to show us.
He gave us a definition of herbarium: A collection of preserved plants, stored, catalogued and arranged systematically for study. He explained that they are vital reference material for plant identification, and allow study of the distribution of plant Taxa, and phenology, which are becoming increasingly important for conservation because of changing climate and habitats. The movement of plants can be traced, and their ability to change flowering and fruiting times to align with changes in climate (called phenotypic plasticity). He explained that this can be a problem for pollinators as they may not emerge when the plants are flowering. Another important use of herbaria is the analysis of samples of DNA, which are are used to improve understanding of evolutionary relationships and update phylogenetic trees.
A summary of the history of herbaria
He showed us a photograph from Victorian times titled ‘Encamped in the Rocky Mountains’, showing Joseph Hooker from Kew, with the botanist Asa Gray beside him, surrounded by plant presses – typical of the very civilised plant hunter explorations at the time. But the preparation of herbarium specimens does go back a lot further. Luca Ghini, at Bologna and Pisa Universities, who lived from 1490 to 1556, is credited with producing the first herbarium – hortus siccus (an arranged collection of dried plants) – when he collected and preserved specimens as reference material for his students studying medicinal uses of plants. Some of his students became influential botanists in the 16th century; Gherardo Cibo, Andrea Cesalpino and Pietro Mattioli. All fundamental figures in the development of taxonomy and plant classification. Gherardo Cibo, a brilliant artist, produced the oldest herbarium specimens that still exist. He created wonderful illustrations for the Italian translation of Dioscorides: De Materia Medica in c.1564. Illustrations in different versions were quite simple woodcuts, and the exciting thing that Gherardo Cibo was able to do, in correspondence with Mattioli, was produce more detailed and accurate plates, no doubt using his herbarium specimens. Chris told us that he always goes back to the original sources with his students and the digitised version of the book, with 401 illustrations, can be seen in the British Library collection online.
Alongside Gherardo Cibo, Andrea Caesalpino was a student of Luca Ghini and he was one of the first botanists to start to use the natural classification system. Plants were classified using artificial classification up until this time, using traits that people put on to plants rather than traits they exhibit, for example lungworts (Pulmonaria spp) are named because their leaves look like lungs, and other plants were named for their medicinal properties. The more natural classification approach involved observing the constituent parts of the plant and arranging them according to their distinguishing characteristics. He also has the second example of an herbarium still in existence, produced in 1550-60, it contains 768 species of plants in three volumes. Caesalpino’s most important publication was De Plantis Libri XVI in 1583, where he produced the first scientific classification of flowering plants. Chris showed us an example of what his classification system would look like, separating trees and shrubs from herbs, a good jump forward.
Today’s herbaria
The amazing building that is the herbarium at Kew, called Wing C; he described as like something from the movie Labyrinth. There is an herbarium in South Africa that was involved in the fires a few years ago, and lots of the plant material had to be moved quickly. So the herbarium at Kew, like most established herbaria, have their fire alarms linked directly to the fire brigade. The new herbarium in Victoria, Australia, has a focus on first nations people collections, with an approach to readjusting the common names of plants. Common names are generally frowned upon as it makes it difficult to standardise the plant material. But when the ethnobotanical side of things is taken into account, people have certain names for plants and there is an element of ownership associated with that, and the use of common names becomes an inbuilt part of that society. So, in Australia they have strived to embed this into their herbarium material.
Arranging an herbarium
Chris explained that there are different ways of arranging an herbarium, and the most important thing is being able to find the plants you are hoping to analyse. When starting to build an herbarium, the best way to arrange plants is alphabetically as this makes it easy to find specimens. As the collection grows, and there are lots of different types of plants and different species, to get more use out of the herbarium and think about comparing plant material, a more systematic approach is better. If you discover what you think is a new species of plant in the field, you would be able to key that down to genus and maybe species. But if it is a regional oddity or distinct different species, you can go to the herbarium and look for where that plant material should be to compare it to. Also, the plant material can be analysed to look at differences and similarities from a molecular perspective. Herbaria also have spirit collections – nothing to do with ghosts – where precious specimens, such as the small orchids at Kew, are stored in a spirit solution of white spirit, glycerol and water (formaldehyde is no longer used). There are carpological collections (seeds and fruit, and parts too large to be on the main herbarium sheet), so for example, pressing a coconut would be difficult, so with the herbarium sheet for the coconut palm would be an associated box. When analysing a specimen, the box would be examined with the sheet. There are also wood collections and Eden has one of these because some of the trees originally in the rainforest biome did not have space to develop a tap root, making them wobbly and a hazard. Some of these were taken out and a wood collection made as they can be identifying characteristics. Also, seeds are important as they can be used in studies of seed dispersal, and pollen records can be kept. Chris said these are useful to forensic botanists solving murders.
Most of the large herbaria focus on a phylogenetic arrangement, where families that are closely related are located in the same place. Chris explained about the work of the Angiosperm Phylogeny Group, botanists who update the taxonomy of flowering plants by mapping their true molecular relationships. The great thing is that using the analysis of physical traits lines up quite nicely with the phylogenetic analysis and there haven’t been any huge scares. However, as more data is added, the phylogenetic relationships do change a bit, and Chris thinks the group are now on version APG V (5). (There is a good article on Wikipedia about the APG). Molecular information on plants is also valuable when investigating new varieties of plants and selecting breeding attributes. For example, with coffee, which is under threat in its natural habitat, studies of close relatives of the plant in tropical west Africa are providing information on developing possible alternatives. Chris explained that, in the Kew herbarium, changes are generally kept digitally and when there is a big rejig, like in 2010 for the new herbarium, the plants are put in order of the latest Angiosperm Phylogeny Group at the time. So, families are arranged phylogenetically, based on how closely they are related both molecularly and physically. And often as well, the global distribution of the species is considered, with different codes given to different regions, for example the UK would be ‘1’, then moving to ‘2’ and ‘3’ for Europe and the Middle East etc.
Type specimens
Chris went on to talk about type specimens as most of these have been digitised and can be viewed online. Type specimens are the actual specimens that ‘anchor’ the name of the plant. The name and description of a species would be based on one herbarium specimen, so these are important, and herbaria do their best to keep these safe. This would be the holotype. It is possible to create a new specimen if something is lost or destroyed, but it is a lengthy process, and there are a range of ‘types’ which anchor a plant to an herbarium specimen. A lectotype is when the person who proposed the name did not actually create the type specimen and this was done later – as sometimes happened with Victorian plant collectors. Neotypes are replacement specimens, and there are others such as epitypes, syntypes, paratypes and isotypes (duplicates of a types specimen). The great thing is, because of access and benefit sharing in the Convention on Biological Diversity, most types are digitised and if there is a complete flora, such as the Flora of Tropical West Africa, every species will have a type specimen associated with it. It is possible to access the plant material online when you are preparing an herbarium specimen to see who has done the same species in the past, and what sort of job they have done. It is useful as it highlights how difficult it can be sometimes, no matter how hard you try, specimens can be black and blotchy, or bits have fallen off, and Chris showed an example of a specimen collected by Charles Darwin – “What a mess”. Also, it shows how important it is to have a label with the correct information because without that you won’t be able to go back and complete or repeat that collection. Chris showed some specimens from the Kew collection and the New York Botanical Garden herbarium and told us that all his students do some research of their chosen species in this way before preparing their own specimen. The New York Botanic Garden has a huge number of specimens digitised with very good taxonomy.
Herbarium collecting rules
Chris told us about cycads, which are protected as they are in danger of becoming extinct because they live in endangered habitats like rainforests and grow slowly and reproduce infrequently. At Kew there is a living type specimen of a cycad, one of the last of its species. Because it is so rare, a dried herbarium specimen cannot be produced.
Most herbaria are associated with a botanic garden, which can negotiate the legalities associated with moving plant material from one country to another. Plant material is protected through what is known as the Nagoya Protocol, which is a biodiversity protocol, and gardens moving plant material need to draw up an access and benefit sharing approach to show how they might share the benefits of having that plant material. There are lists of what can’t be moved and what can be moved, arranged in appendices, and for endangered species it is usually easier to establish an herbarium in the country of origin rather than move plants. Luckily, through digitisation we can now have access to those specimens. Moving through the appendices the plant material becomes more accessible from an international perspective. The protocol is there to protect countries and their biodiversity from biopiracy. Be aware that if you are thinking of collecting overseas, there have been some very serious fines and prison sentences for people trying to smuggle plants out of some countries. So collecting plants overseas requires a lot of planning before going on the trip, you need to have prior informed consent (PIC) and mutually agreed terms (MAT), but this is good because if it is done properly you get the plant, and support from local communities.
Plants in the UK are protected under the Wildlife and Countryside Act, where those listed as Schedule 8 plants, such as bluebells and orchids, are tightly protected and require a licence to collect. Invasive plants, such as knotweed, are Schedule 9 and can probably be collected for herbarium specimens without much difficulty. There are guidelines available on collecting specimens, including a good leaflet – Code of Conduct – which can be downloaded from the Botanical Society of Britain and Ireland (BSBI). There is also the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species which is the Red Data Book containing details of endangered and threatened species. Chris said that, for artists, having the information on the plant would add to the story of the painting. The main thing to remember is that it is important to have permission from the landowner before collecting specimens. It is illegal to pick, uproot or destroy any plant without permission. There was some discussion on foraging eg for blackberries, and being mindful of where they are growing is important. (For example, The National Trust allows foraging on its land for personal use but requires consent on any Site or Area of Special Scientific Interest).
Collecting plants
Chris went on to talk about collecting plants and explained that having the right data was important so that the collection could be repeated if needed, for example if a specimen disintegrates. It also means that distribution maps can be produced. Date, time and location – the grid reference – should be recorded (occasionally What Three Words). Notes on associated features and associated species are also useful, ie what is growing around the plant, to build the picture of the community. Noting how many plants, and flowers and fruits present is also important to include all relevant stages of the lifecycle of the plant.
If there is only one plant, record where it is and perhaps go back and revisit it when there may be more. If there is a variable population, select a specimen that has all the distinguishing characteristics of the species, and it is useful to pick out a good and poor example, as sometimes what is representative of the species might look somewhat degraded. Dead specimens are not good choices.
When preserving the specimen, Chris recommends keeping one plant on one page, different plants should be on different pages, even if they are from the same population. Fruits collected from the same plant at a later date should also be on a separate page. There is also the challenge of things falling off and these can be kept in a paper capsule with the specimen as these are often useful when analysing the plant. Each specimen will have a jewellery tag with a collection number, species and date. Collection numbers are personal, eg Chris would have CB102, and the tags should go on the specimen straight away before putting it in the press. The description would go in a notebook and this would be used to create the label for the specimen. The tag will stay with the plant in the herbarium.
Collecting equipment should include a penknife, small trowel, secateurs and possibly a pruning saw if it is for woody specimens, clear plastic bags without holes in the bottom (Eden use clear eco bin bags), and a camera. Also, newspaper and blotting paper with a plant press. Selected specimens should be jewellery tagged and put carefully in the bags, then moved to the plant press when it is convenient, being careful to not open the press more times than needed, so that previously pressed plants are disturbed as little as possible. Relieving the pressure can cause some plants to come apart.
Choosing a specimen
When choosing a specimen think about how to include the distinguishing characteristics, such as how the stems and leaves are arranged. Stipules can be really annoying as they can fall off when the plant is handled or dried, but there is always a scar left. Bits that fall off can be collected and put in the paper capsule. Monecious plants, with male and female flowers on the same plant, can be tricky because ideally, they should all be represented on the same page. This is sometimes difficult and needs a separate sheet for the same plant, created at the same time. In this case label them A and B with the same number. Diecious plants, having male flowers on one plant and female flowers on another, would be completely different collection numbers because they are from different plants. Labels are produced for the mounted specimens with the collection number, date, location (this can be associated with a point on a map if necessary), scientific name and common or local name. Colour and scent can also be recorded, these are tricky, and we have previously had discussions with Chris about how to record colour and whether the RHS colour charts should be used. Chris asks his students to buy the book – Kew Plant Glossery by Henk Beentje – which has useful colour terms in the back, providing a reference to build on. He reminds them not to use digital sources for colour as these have a lot of variation. The Flori has a set of the RHS colour cards but for herbarium specimens with an associated painting, the colours in the painting are agreed to be those of the specimen. Chris said some sort of standardisation for colour is good. The scent of a plant can be different at different times and can be recorded if significant and possible. Photos can also be kept as useful reference material, and a note of local uses of the plant, if thinking about the ethnobotany. Labels can be quite extensive with a lot of information. It is also possible to do a slash test on woody specimens and make a note of the colour of sap, the colour of wood, etc. Other information on habitat such as altitude, aspect and soil can also be recorded. Chris showed some examples of labels with good data.
The scientific names of plants need to be written correctly. The genus always starts with a capital letter, and the species lowercase, with the genus and species always in italics or underlined. The variety or subspecies would need to be included and not be italicised; however the subspecies epithet would be italicised. (For example: Digitalis purpurea var. maculata ‘Superba’ indicates a cultivar ‘Superba’ – cannot be produced from seed – of the foxglove variety, a distinctly spotted form.) The family names will either be completely capitalised or just have the first letter in capitals. Names on labels can stay for several hundred years before being reviewed and often labels end up with lots of annotations, as on Darwin’s specimens. Notes also need to include reference to any carpological boxes or other materials.
Drying and pressing
Newspaper and corrugated cardboard are the best materials to use for drying and pressing a specimen. Hard cardboard or frames can imprint on fleshy specimens, and when putting one plant on top of another, care is needed to ensure that they are not going to imprint and affect the pressing of each other, so use pieces of card between thicker specimens. It is easier to press slightly wilted material, so a little time between picking and pressing is useful. Chris does not recommend using microwaves for drying specimens as they tend to give a patchy result. Using some uniformly heavy objects on the specimens can help with pressing, and warmth is also used sometimes, but take care as too much heat can cause damage. Chris described visiting an herbarium in Malawi where it was like walking into a tanning salon. There was some discussion about pressing different plants. For example, with Kniphofias some packing material can be placed around the flower head to maintain the original shape, and any flowers that fall off can be placed in a paper capsule. Chris had pressed a Kniphofia in the field and cut some of the back off the flower head, and removed most of the inside of the corm, before pressing it. It is hard to stop some of the flowers falling off, and possibly a desiccator would do a better job of drying the plants. Cacti are very difficult and pressed ones can look like a leather experiment gone wrong. Some plants may need to be cut in half in order to get a good, pressed specimen. Cross sections can also be pressed.
Specimens should be positioned in a life-like arrangement that is true to the habit of the plant. Characteristics that are distinguishing for the plant should be visible, for example hairs on the underside of a leaf. Leaves can be folded over or parts cut off if they are large. Try to include the front and back of the flowers, and the way leaves and flowers are attached, similar to what would be included in a botanical illustration of the plant. Chris showed some examples of good layouts, suggesting that if there are too many leaves some can be removed as long as the petioles remain and there are enough left to represent the leaf positions and the way the plant grows. Also, it is important to check that any bulbs included are dead as they could start to grow. Scoring it in half or putting it in boiling water will prevent this happening. Potato peelers are useful to remove the back of thick stems.
Layer the specimen with blotting paper, newspaper and corrugated cardboard in the plant press. It needs to be checked after 24 hours and re-arranged if necessary, using fresh newspaper if required. Newspaper works well because it is quite absorbent and cheap. When handling any pressed specimen Chris recommends treating them as though they could explode and being very careful – always have a piece of card underneath and use both hands.
Drying time
Drying times vary depending on the specimen and it is best to overestimate how long it will take to make sure it is ready. Before mounting the pressed plant will need to be frozen for a period of time to kill any remaining wildlife, such as thrips, that could damage the specimen. Chris advises carefully placing the specimen in a plastic bag, sealing it, and leaving it for at least 5 days in a conventional freezer, keeping it as dry as possible.
Chris put out on display some of his students’ herbarium specimens from the ethnobotany module. He explained how they had mounted their specimens using acid free paper and card, and used neutral pH adhesive, suggesting the best way to spread a fine layer of the glue is with a folded piece or paper or card, as plastic dabbers can be a bit abrasive, and brushes can carry too much. Small pieces of linen tape can be used to keep areas that might move in place. The tags on the specimens should be left attached.
Sally got some of the Flori specimens out to show Chris. These are kept in cabinets in the Foundation Building. The guidelines for preparing and mounting specimens are in the members area of the EPFS website and have been updated to reflect the recommendation of Chris that the specimens are frozen for at least 5 days.
Materials for mounting specimens for the Flori are also available: Acid free card for mounting specimens, acid-free folders to put them in, pH neutral glue, thread and linen tape.
Chris referred to a book by Diane Bridson, called the Herbarium Handbook, the latest edition of which was published in 2007. There is now a new Kew book with the same title – The Herbarium Handbook – edited by Nina M.J. Davies, Clare Drinkell & Timothy M.A. Utteridge, published in October 2023, which keeps the “essence of the original” but includes articles from many authors “setting out best practice in herbaria of any size or location”.
Other useful herbaria references given by Chris Bisson complied by Jacquie Ashton.
De Materia Medica by Dioscorides translated into English
https://ia802907.us.archive.org/16/items/de-materia-medica/scribd-download.com_dioscorides-de-materia-medica.pdf
Cesalpino’s taxonomic system of Plantae from De Plantis Libri XVI (1583)
https://www.reddit.com/r/botany/comments/vku1zd/discussion_cesalpinos_taxonomic_system_of_plantae/?utm_source=share&utm_medium=web2x&context=3
Kew Herbarium
https://www.kew.org/science/collections-and-resources/collections/herbarium
Kew Data Portal for herbarium specimens at Kew
https://data.kew.org
NYBG C.V. Starr Virtual Herbarium
https://sweetgum.nybg.org/science/vh/
Bebber et al. (2010) Herbaria are a major frontier for species discovery.
https://www.pnas.org/doi/10.1073/pnas.1011841108
Convention on International Trade in Endangered Species of Wild Fauna and Flora
http://cites.org
Convention on Biodiversity
http://www.cbd.int
Joint Nature Conservation Committee
https://jncc.gov.uk
Schedule 8 the Wildlife & Countryside Act 1981 (plants which are protected)
https://www.ukwildlife.com/index.php/wildlife-countryside-act-1981/schedule-8/
BSBI (Botanical Society of Britain and Ireland) Code of Conduct for the conservation and enjoyment of wild plants
https://bsbi.org/wp-content/uploads/dlm_uploads/Code_of_Conduct.pdf
IUCN Red List of Threatened Species (to check the status of a species)
https://www.iucnredlist.org
To download conservation designations for UK Taxa
https://hub.jncc.gov.uk/assets/478f7160-967b-4366-acdf-8941fd33850b
Botanical Society of Britain and Ireland (article on collecting and pressing specimens)
https://bsbi.org/wp-content/uploads/dlm_uploads/Collecting.pdf
Botanical Society of Britain and Ireland (Code of Conduct leaflet)
https://bsbi.org/wp-content/uploads/dlm_uploads/Code-of-Conduct-v5-final.pdf
National Trust (Foraging Code of Conduct)
https://www.nationaltrust.org.uk/who-we-are/about-us/our-policy-on-foraging-for-wild-food#:~:text=Foraging%20code%20of%20conduct,-To%20ensure%20that&text=Please%20only%20pick%20for%20personal,specimen%20before%20picking%2C%20not%20afterwards.
JNCC Red Lists in Britain
https://jncc.gov.uk/our-work/red-lists-in-great-britain/
