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A guide to collecting herbarium specimens
ferns and their allies

Prepared by Jim Croft (
General principles
Preparing specimens
Drying specimens
Field notes
Lodging specimens

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.

Some general principles

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:

Preparing specimens

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:

Drying specimens

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.

Field notes

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:

Detailed instructions in the use of a typical field book are available.

Lodging specimens

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.

See also:

Other resources on plant collecting

Updated November 1999 by Jim Croft ( )