A guide to collecting herbarium specimens
ferns and their allies
The pteridophytes, or ferns and related plants, are small to large, mostly medium-sized vascular plants and are generally stored and curated in herbaria in much the same way as the flowering plants and conifers. They are prepared by presssing and drying and are mounted on herbarium sheets about the size of a tabloid newspaper, with labels derived from field notes; bulky material and material preserved in spirit is generally stored and documented as they are in the rest of the herbarium. Thus the techniques for collecting, preparing and mounting pteridopyte specimens are much the same as those for other vascular plants and in many cases the task is easier as ferns are generally not as rigid as woody plants and the fronds are usually flat or two-dimensional.
Herbarium specimens are collected for a variety of reasons but they nearly all involve the need for physical documentation or evidence of, for example, plants that grow in a certain area or locality; distribution of known plants, vouchers for ecological, ethnobotanical, land-use studies, etc. or for scientific or general curiosity. The idea behind collecting herbarium specimens is to produce a near permanent object that will last for centuries, one that can be reliably and completely identified, and one that is associated with a range of useful information. Some things to remember in collecting pteridophyte specimens:
- Ensure you have permission to collect. Permission is generally required to collect plant specimens from the wild. Prior permission and collecting permits and must be obtained from relevant authorities; each country and State has its own agency for regulating and monitoring plant collecting and sometimes different permits may be required for National Parks and State forests. Always endeavour to let the local manager (rangers, foresters, etc.) know you are collecting in their area and that you have permission to do so; you may need to ask the local managers to give you access to the area. Many interesting pteridophyte habitats reside on private farming property. Always seek permission of the owner on the property before venturing onto their land to collect plants. Special permission will be required for indigenous or traditionally managed land. Some authorities may imose restrictions on what taxa how much material you are permitted to collect.
- Collect fertile material. Like the flowering plants and conifers, much of the classification of pteridophytes is done on the structure and arrangement of the reproductive parts of the sporophyte: the sporangia and sori, often found as brown or black dots or powder on the underside of the fronds. In nearly every case infertile fronds lacking sporangia will be difficult to compare and identify and will be useless as herbarium specimens. Many ferns have dimorphic fronds (fertile and sterile fronds of different shapes and sizes); ensure that you collect both the sterile fertile fronds for each duplicate specimen.
- Collect stipe bases and rhizomes. The presence and structure of scales and hairs at the base of the stipe (leaf stalk) or on the rhizome (main stem) is often critical for the identification of ferns, from family to species level. Every attempt should be made to include stipe bases and associate hairs and/or scales as part of the specimen. This may be done as part of the mounted specimen or as a separate tagged item. The internal structure of stipe bases and rhizomes often important diagnostic characters identification. Sometimes these collapse when dried but resussitation is possible; a description, sketch or photograph is often helpful. Sometimes rhizomes have distinctive branching patterns (dichotomous, anisotomous, unbranched, etc.) and this should be noted.
- Attempt non-destrcutive sampling. Specimens are usually collected in connection with a project with an intention of lodging them in a particular herbarium. This may be a requirement of the project or there may be a requirement of the collecting permit to lodge duplicate specimens in particular herbaria; additional duplicate specimens may be required for special purposes. However, care should be taken not to endanger plants or populations in the field. For large species, fronds and portions of rhizomes should be carefully removed with secateurs or a sharp knife so as not to destroy the grwoing apex and thus the whole plant. Try not to remove two many fronds from one plant. With smaller species it will be necessary to collect whole plants and a sample of a larger population. Try to avoid collecting the only pant in an area and try to leave sufficient individuals to allow the area to be repopulated.
- Avoid mixed collections. When making a specimen of a number of individuals from a population of ferns, pay particular attention to not collecting two (or more) different species as part of the same gathering. With the smaller epiphytes especially, it is not uncommon for a number of related and superficially similar species to be growing side by side on the same tree trunk. If you inadvertently make a mixed collection, separate the component species after the event and assign each of them 'A' and 'B' (etc.) numbers.
- Make field notes. Good field notes, generally made in a field book, are an essential part of any herbarium collection. The are needed to establish the uniqueness of a collection, to localize the specimen in time and space, and to provide information for botanists trying to create a complete picture the structure and distributions of the species. The more information you can provide, the more valuable your collection will be; a well prepared specimen will last for centuries and may end up as the only remaining record of a species occurrence for a region.
- Take photographs. Photographs of the live pteridophyte are a valuable addition to the herbarium. Long lasting colour slides (eg. Kodachrome) are preferable to negatives and prints. These are particularly useful in showing the habit and three dimensional arrangement of the plant and its fronds, the colour and texture when fresh and the overall shape of large plants or fronds. Pteridophytes often grow in moist dark places places where photography is difficult; it will probably necessary to use a tripod and/or flash to produce a good photograph. Pteridophytes are often growing close to or entangled with other vegetation and effort will have to be made to isolate the plant from others; black (or white) cloth back drops are useful in this regard.
- Process material promptly. Ferns are mostly delicate and wilt or damage easly. Specimens should be placed in the press as soon as possible and not carried around in bags for extended periods. Unpressed specimens caried around in polythene bags tend to compact and crush. Moreover on hot days specimens in plastic bags sweat and may discolour in the heat. Field notes should be written at the time since details are often forgotten or confused when trying to reconstruct notes after the event. This is especially important when many collections are being made from a number of different localities.
Typical material from vigourous and healthy specimens should be selected, and as far as possible these should be free of physical and insect damage or fungal or gall infestation. Additonal material may be selected to show the range of variation present in an individual or a population, or peculiar forms or growth patterns. If rhizomes or rootstocks, especially underground ones, are collected, soil, moss and other extraneous material should be removed.
Once collected, specimens must be prepared for pressing and drying so as to best present those characters that are useful for identification. This should be done as soon as possible after collection, before fronds have a chance to wilt. Fronds should be arranged so that both upper and lower surfaces are visible and adequely display the diagnostic features. Large fronds may have to be variously folded or cut into a number of pieces to fit on the herbarium sheet. Large stipe bases and other awkward rhizome may not be able to be mounted easily and have to be stored separately. To avoid mixing of specimens, tags with collectors initials and field number should be attached to each component, or at least the first and last sheet of a specimen.
The specimens are placed bewteen sheets of folded newspaper to separate the speciems and components from each other. If it is expected that some time will pass before plants can be placed n a drying press, an additonal sheet of newspaper should be wrapped around all the components and duplicates of a single collection to reduce the chance of specimens becoming mixed.
Ferns and their allies exhibit a wide range of habit and structure and a number have special preparation requirements:
- Aquatics. The surfaces of aquatic pteridophytes should be dried as much as possible before presssing, otherwise papers, blotters and corrugates will be unduly moist before the drying process starts. When drying, some may tend to stick to the newspaper, and it may be a good idea lay them out between layers of tissue paper. With rooted aquatics, wash away as much of the mud and silt from the rhizome and roots as possible before placing in paper and pressing.
- Cheilanthes and other resurrection ferns. Cheilantesand some related genera of Adiantaceae sens. lat. are adapted to grow in dry and relatively harsh environments. They grow during moist periods and shrivel to an almost crisp state when dry. Following rain they can imbibe water, come back to life and contine growing. Specimens of these species can be and are often made in the crisp state, but better specimens that are easier to study can be made by soaking the plant in water overnight, and then pressing and drying the material once it has swelled and become supple. The same technique can be use to reprepair specimens that have dried and shrivelled in the between when they were collected and when they were got to a press.
- Ferns with large fronds. Fronds larger than a folded sheet of newspaper will have to be reduced in size to make a suitable specimen. This may be done by trimming, folding, folding and trimming, cutting into smaller bits, or any combination of these. The longest pinnae of the fronds of most species can be made to fit on a sheet by folding in half, or in a zig-zag 3 - 4 times; to reduct the clutter and confusion on the sheet, all the pinnules on one side of the pinnae can be removed with secateurs. Try to arrange the elements so that both surfaces of the frond are visible. When preparing a specimen with several components, it is very important the components do not become disassociated; liberal use of numbered tags is encouraged. It is not necesary to keep all the parts of a large fern, altough some botanists have done this in the past; it consumes undue amounts of space in the herbarium. Gernally it is sufficint to keep the tip of the frond, a middle or largest pinna, a basal or smallest pinna (often the basal pinna is the longest), and notes about the length of the frond, the width of the frond and the length of the stipe (from the attachment to the rhizome to the first or basal pinna). In some large ferns the basal side of the basal pinna is greatly enlarged and may itself bear pinnae; the presence of this should be noted as it may not be obvious in dried and mounted specimen. If it is possible to describe the overall shape of the frond (elliptic, ovate, lanceolate, oblong, deltoid or triangular, rhomboid or diamond-shaped, pentagonal, etc.), do so.
- Climbers. A number of ferns are climbers, ascending into the crowns of trees. They are generally big plants, and are collected in the same manner as other ferns with large fronds. They may have either a long-climbing rhizome running up the tree, or a terrestrial rhizome and long stipe and rachis that scrambles upwards. In each case, a portion of the rhizome with its scales and/or hairs should be collected. Make notes of the overall size of the plant, the size of the fronds or pinnae where this is not going to be obvious from the pressed specimen, the spacing of the fronds or pinnae, how high up the tree the plant climbs, whether the fronds are erect, horizontal or pendulous, etc. Often in climbing ferns, from or pinnae low on the plant tend to be sterile, while those higher up or near the apex of the rhizome tend to be fertile; if this is the case it should be noted. In some species of climbers, the lower fronds (or bathyphylls) are quite different in appearance to the upper fronds (or acrophylls); if present this fact should be noted and examples of both types of fronds should be collected.
- Dicksonia, Cyathea and other 'Tree ferns'. The fronds of tree ferns can be over 1 - 3 m long and are collected and prepared in much the same manner as other large-fronded ferns. Stipe bases are particularly important and the bottlom 20 - 30 cms of stipe should be collected. Stipe based may be persistent or deciduous; this fact should be noted. Generally a middle pinna will fit on an herbarium sheet once folded in half or tri-folded. If possible a basal pinnae should be collected, or at least its length recorded; the length of the stipe to the lower most pinna should also be noted. Tree fern produce their fronds in a number of ways. Their fronds may be in distinct whorls or produced more or less continuously; this fact and the number of fronds in each whorl should be noted. Tree ferns should not be chopped down to get at the crowns; trunk samples while are attractive and interesting are for most purposes not necessary - collecting them kills the plant.
- Marattiaceae Marattia and Angiopteris. Marattia and Angiopteris are collected in much the same manner as any other large-fronded fern. In spite of their often huge size and fleshy succulent structure, they dry quickly and well in the press. The swollen stipe bases with their fleshy auricles are a particular challenge: these may be about the size of a large horse's hoof and may be cut in half to reduce the bulk; even so they will take a long time to dry completely.
- Polypodiaceae. These ferns are mostly high epiphytes and have adapted to a habitat that may often be subject to harsh sunlight and water stress. Their fronds are often stiff, fleshy and leathery and have the ability to retain water during hot and dry periods. Thus they are the most difficult ferns to dry in the plant press and will take several times longer than ferns that are much more fleshy or succulent. Heat is required but too much will cause them to brown; it is important to make sure that air is constanty moving and warm moist air is able to escape. Dipping the plants in alcohol or petrol for a minute or two kills the surface cells, breaks down waxy cuticles and allows the specimen to dry more quickly; if you do this, it should be noted on the field label.
- Waxy or glaucous coverings. A diverse range of unrelated pteridophytes produce waxy covering on their leaves, fronds (mostly on the underside), and/or on their rhizomes; examples are Dipteris, Pityrogramma, some Cheilanthes. This covering ranges from a greyish or bluish glaucescence, to a white, cream or yellow floury covering. The presence of such a covering is often an important diagnostic character. Certain treatments may break down the structure of the wax and it may not be visible in the dried specimens. Treatment in ethanol and other solvents may disolve the wax and excesive heat may melt it and make it invisible. The presence of glaucescence or other powdery covering should be noted in the field notes, as should any treatment that might affect it.
- Hymenophyllaceae or 'filmy ferns'. Because of their generally small size and delicate nature, the many of the filmy ferns require special attention. To avoid bits getting lost, it is a good idea to place the specimens in numbered paper packets or envelopes before placing them in newpaper in the press for drying. Hymenophyllaceae dry within a few hours if you need to make space in the press. Once dry the fronds are light and fragile and should be handled carefully, out ot the wind.
Herbarium specimens are preserved simply by removing water contained in the vessels and cells. This not only kills the plant cells and prevents the proces of autolysis (break-down of cells and tissue structure when they die) but prevents the growth of fungi and attack by other organisms causing decomposition. Drying should take place as soon as and as quickly as possible while the plants are being pressed, and is usually accomplished by the movement of mildly warm (not hot) dry air around the specimens. Air movement is more important and more effective than heat and sheets of corrugated cardboard interleaved between each specimen is very effective in allowing moist air to escape. Heat without air movement will stew and discolour the specimens and may even allow them to go mouldy and rot in the press. This is a particular problem with the fleshy and leathery genera of Polypodiaceae that have particularly good water retention mechanisms, a particular adaptation to an exposed epiphytic habit. Excessive heat may also denature the DNA and other chemicals retained in the specimen and reduce its usefulness for future studies of these substances. Most other ferns and fern allies lose water from their tissues readily and dry rapidly in the press. It is imortant to ensure that moisture leaving the specimen is removed quickly either by air moving through the press, or by dry blotting paper which is changed at regular intervals.
It is usual to return plant pressed to the herbarium for drying in specialy designed plant driers. Drying plants in the field can provide a challenge. In dry environments, driving with the plant press tied securely to the roofrack can be particulalry effective. In humid environments, external heat as to be applied, either from a simmering gas stove, or kerosine lamps; the press is suspended above the heat source and the rising warm air passses through it; a sleave or skirt tied around the press will ensure that warm air does not escape. Specially designed portable field driers are available. In tropical conditions corrugated aluminium is used in addition to corrugated cardboard to ensure heat is distributed evenly through the press.
In extreme remote tropical situations drying in th field may not be possible. Specimens pressed in paper can be stored in plastic bags or sleaves and the paper saturated with ethanol. Specimens stored this way will keep for many months and can be dried at a later date. However this practice discolours the specimens and is not encouraged. If you do treat specimens this way, note details of field preservation on the field label.
Most ferns will be dry after 12 - 24 hours. Feel for claminess or coolness to touch - if the paper is crisp dry, the specimen will very likely be dry as well. Once dry it is important to keep the specimens that way, storing them in newspaper, flat in a box, perhaps with a few interleaved sheets of corrugated cardboard to reduce the likelyhod of specimens in the pile crushing each other.
A field book should be maintained with separate field notes prepared for each specimen, with a collectors number corresponding to the number on the tag on the specimen components. Field notes should contain information not immediately obvious from the dried specimens. This information will be used to prepare the herbarium label and in many cases it will be sorted in databases and used for a variety of scientific purposes so it is important that it is complete, accurate and unambiguous. All measurements should be metric and as far as possible, standard descriptive terms should be used.
Typical information includes:
- Collectors name, associated collector(s) name(s)
- Collectors sequential field number (must be unique)
- Collection date
- Field identification (family, genus, species if possible)
- Locality (country, state/province, location relative to a named place)
- Longitude and latitude (from map, gazetteer or GPS)
- Altitude (in m, relative to sea level)
- Depth (in m, if aquatic)
- Habitat (aspect, substrate, soils, vegetation, cover, exposure, etc.)
- Notes about the plant (abundance, habit, size of plant and components, arrangement of frond and other parts, distinctive colours, smells, exudates, etc.)
- Other notes (associated species, local uses, local names, pests, special preparationetc.)
- Material collected (dried specimens, separate rhizomes, spirit material, photographs, living material, etc.)
Detailed instructions in the use of a typical field book are available.
Specimens should be lodged in a major and well curated herbarium with a long-term commitment to the flora of their region, making botanical material and information available to the scientific community through specimen loan and exchange programs and through on-line access to their databases. If not a requirement of the collecting permit, it is courtesy to lodge a duplicate specimen in the national herbarium of the country and in appropriate state or regional herbaria (and in a host herbarium if they are assisting your work). It may also be desirable to send duplicate material to to other herbaria in which experts in particular plant groups are working. With small species, several plants should be collected to adequately represent the species a single sheet. Enough duplicate material should be collected to meet these requirements, without endangering the natural populations.
- Permit requirements for the collecting of Australian plants and animals
- Introduction to collecting plants from the Australian National Herbarium
- Field book guidelines fom the Australian National Herbarium
- Herbarium specimen mounting guidelines from the Australian National Herbarium
- Introduction to herbarium curation from the Australian National Herbarium
- Public Reference Herbarium at the Australian National Botanic Gardens
- Plant Photograph Index at the Australian National Botanic Gardens