Saturday, 26 November 2011

Introducing the herbarium

A herbarium is one of the main tools for research and documentation of plant biodiversity.  It sounds like a garden, and in fact an old name for a herbarium is hortus siccus, or dried garden.

A herbarium is a collection of dried and pressed plant specimens.  The first herbarium is thought to have belonged to Luca Ghini, an Italian professor of botany, in the 16th century.  Early herbaria were kept in bound books, but mounting each specimen on a separate card—we call them "sheets"— means the specimens can be rearranged and studied separately, and it minimises damage.

The specimens are pressed only to keep them flat while they dry.  It's the drying that preserves them.  The best specimens have all the plant parts represented, so they can be studied, but this gets tricky with large plants.  With palms and tree ferns, where a single leaf can be several metres long, there are compromises to be made.  Kept dry and free of pests, a herbarium specimen can last for hundreds of years.  Several New Zealand herbaria have specimens collected on Cook's first voyage in 1769, and they're still in good condition.

The label on a herbarium sheet is very important.  It identifies the plant, tells where it was collected (now with GPS reference), what habitat it was growing in, who collected and identified it, and when, and provides notes (e.g., flower colour, abundance, scent, etc.).

The main advantage of a herbarium is it brings a large sample of different species together in one place where they can all be compared.  And it brings a large sample of individuals together too, sampled from different locations and different habitats.  While field work is important in biodiversity, the detailed research and discovery often takes place in the herbarium.  I remember sorting buttercup specimens (Ranunculus) with the late Tony Druce in the late 1970s.  We found an odd specimen in the Ranunculus hirtus folder that we thought might be an unidentified introduced plant.  Among the specimens of the next species we looked at, we found another, similar, one.  By the end of the day we had a pile of specimens of what we were now sure was an unnamed native species, now called R. altus.  It's a common plant on montane forests of the South Island, on disturbed sites like old landslides.
Ranunculus altus at Rough Creek, Arthur's Pass National Park.
We use herbarium specimens all the time in taxonomy.  Most often we use them as references to check our identifications.  In very critical cases, we can go back to the type specimens, which define the usage of a name.  We also use them when we describe species for publications.  We can even extract chemicals, including DNA, from herbarium specimens for study.

Another important role for herbaria is to document observations.  Let's say I observe red admiral butterflies pollinating Veronica stricta.  I can report that in a scientific paper, but how can the reader be sure of my identification?  If I collect a specimen of the actual plant, then even if I'm wrong it can be checked and if necessary corrected.

Modern herbarium label data are becoming databased, so that on line searches for information are increasingly possible.  Thus we can map distributions, and compare these with other information in geographic information systems.  Traditionally, herbaria have been organised taxonomically, following the scientific classification system, but databasing allows information to be assembled using other parameters, like location, habitat, flowering times, or growth forms.  If you cared, you could generate a list of dicotyledon trees growing in Canterbury above 500m altitude that flower in January.

New Zealand has three large herbaria, at Landcare Research, Te Papa, and the Auckland Museum.  There are smaller ones at other research institutes and universities.  They collaborate through the New Zealand National Herbarium Network. Overseas, there are many much bigger collections, like those at Kew, Paris, Berlin, St Louis, and New York.  The herbarium is an essential tool for studying and documenting plant diversity, and a valuable resource for its conservation.

Wonderful as they are, herbaria have their imperfections and problems, which I intend write about in future blogs.

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