1. Introduction
An herbarium is a collection of preserved plant specimens. Much of what an herbarium
store is specimens of pressed and dried plants mounted on sheets of paper. Plant drying became popular in the 18th century, long before the
invention of photography, when a dried, pressed plant sample was one of the only ways to
see what a plant looked like if it was impossible to see it in person. Botanical drawing and painting was the other main two-dimensional method of depicting plants, and while artistic renderings can be highly detailed and attractive, herbarium specimens have some advantages over them. First, anyone can make them, even someone who absolutely cannot draw. Second, they are by definition true to life. Botanical artists use many conventions to condense a plant's life history into a single image; an herbarium specimen can show a plant as it was at one and only one moment in time, and only at its actual size.
Botanists use herbarium specimens as reference materials. Herbarium specimens are fundamental to the field of plant taxonomy because they are used to describe plant species. Most named species of plants can be linked back to a single herbarium specimen that contains the first definitive use of that plant's scientific name. This sort of specimen is called a "type specimen." Scientists studying plants in the field often make herbarium specimens called "vouchers," which are samples of plants growing at a particular place and time. Herbarium specimens are also useful for studying the geographic distribution of plants, the changes in vegetation over time, and for identifying plants in the field; an herbarium specimen can show more detail than a photograph, making it easier to see venation and other plant structures.
2. Sarracenia
This page contains specimens from four species of the genus
Sarracenia, a carnivorous
plant commonly known as the pitcher plant.
An herbarium specimen from the Natural History Museum, London.
[ link to interactive view ]
Pitcher plants thrive in bogs. Because their environments tend to be low in
essential nutrients such as nitrogen, pitcher plants have evolved an unusual method of
acquiring these minerals - they capture insects, dissolve their bodies, and consume the
nutrients from their flesh.
A pitcher plant consists of a long tube open at the top, usually with a little flap
above it that functions as an umbrella, keeping out rain. The plants attract insects with
scent and nectar. An insect that is so rash as to land on the lip of a pitcher plant
will find itself slipping into the mouth of the tube, which is covered with
slippery wax. The tube itself is lined with slippery, downward-pointing hairs that send the insect sliding to the bottom and prevent it from climbing back out. At the bottom of the tube is a soup of
digestive enzymes that dissolve the unfortunate insect's tissues and make them available to the plant.
An example of Sarracenia, split open to show structures
[ link to interactive view ]
Sarracenia grow only in North America, mostly in the southeast. These plants would have
been new and exciting discoveries to European explorers in the late 18th century. John
Fraser, a Scottish botanist who explored the Appalachians in the 1780s, collected
specimens from four different species of Sarracenia, both pitchers and flowers. He dried
and pressed the plants and delivered them to London, where they became part of a bound
volume of herbarium specimens common known as the ‘Walter Herbarium’,
housed in the Sloane Herbarium of the Natural History Museum, London. (The consensus at
this date is that the ‘Walter Herbarium’ is not actually a collection
of specimens assembled by Thomas Walter and is not in fact the basis of Walter’s Flora Caroliniana (1788), the first published volume of American
plants that used the then-new system of binomial nomenclature to identify species.) (Ward 2007)
These four specimens appear on a single page of the Walter Herbarium. The species
represented are the extremely long-tubed
Sarracenia flava (Detail A), the shorter, narrow
Sarracenia rubra (Detail B), the short and wide
Sarracenia minor (Detail C), and the
chubby
Sarracenia purpurea (Detail D). Each specimen is labeled by hand; the handwriting
might be that of Thomas Walter, who had possession of the collection, or it could be that
of Fraser (Detail E).
Detail A: Sarracenia flava
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Detail B: Sarracenia rubra
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Detail C: Sarracenia minor
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Detail D: Sarracenia purpurea
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Detail E: A hand-written label, perhaps by Thomas Walter, or perhaps by
Fraser
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Note that both Sarracenia rubra and Sarracenia minor are also identified with labels
made on a modern typewriter. These labels might have been added in the 1950s or 1960s
(Sloane Herbarium curator Mark Spencer is not sure when). They mark these
specimens as type specimens used in the Flora Caroliniana. This means that these two
specimens were used to identify those particular species in Walter’s flora, a book listing
and describing the plant species of the Carolinas. As it happens, recent research has
nixed that claim. Ward argues that Walter did not use these specimens in preparing the
flora, and believes that none of the specimens in the Walter Herbarium should be
considered type specimens. (Ward 2007)
A typewritten label identifying the plant differently from the handwritten
label.
[ link to interactive view ]
The plant labeled as
Sarracenia minor on the typed label is called
Sarracenia
lutea on the older, handwritten label. Apparently the name
Sarracenia lutea was never
published, and subsequent scholars concluded that this specimen corresponded with the
S.
minor of Walter’s flora. (
Harper 1903)
The specimens are affixed to the page with narrow strips of linen paper – essentially
tape. These hold the dried plants in place without gluing them down entirely. It was also
common for people preparing herbarium specimens to sew them in place with needle and
thread. Whoever prepared this page took great care in laying out the specimens to fit
several on the page while still displaying them to best advantage. He was forced to fold
the largest specimen in half to make it fit on the page; no book page is big enough to
accommodate a meter-tall plant. Each of the plants is accompanied by a flower. This means
that the collector visited the growing sites in early spring, when flowers
appeared.
A flower held in place with cloth strips.
[ link to interactive view ]
Sarracenia still grow in the Southeast but are highly endangered due to loss of their
particular boggy habitats. These
Sarracenia rubra Walter ssp. Jonesii (Wherry) Wherry,
mountain sweet pitcherplant, a subspecies of Walter’s S. rubra, growing in western South
Carolina, are one of three pitcherplant species listed as Federally Endangered under the
U.S. Endangered Species Act.
Sarracenia growing in the wild.
[ link to interactive view ]
3. Rhynchospora
This is a specimen of
Rhynchospora fascicularis (Michx.) Vahl, commonly called fascicled
beaksedge, a type of grass-like plant common in the Southeastern U.S. This specimen was
collected in 1948, and what a difference 160 years makes!
[ link to interactive view ]
First look at the label. See how much more information it contains than the labels in the Walter
Herbarium. The specimen comes from the herbarium of NC State College in Raleigh, and it
was part of the college’s collection of plants of North Carolina. (This specimen currently
resides in the Museum of Natural History, London.) This specimen was collected by R.K Godfrey in Brunswick County. Godfrey found
this particular plant in a shrub-bog between a road and the Inland Waterway, a channel
that runs parallel to the Atlantic coast, which means that this plant was growing very
close to the Atlantic Ocean. The plant was growing midway between the towns of Southport
and Supply. (We could drop a pin more or less where he was:
34.017500,-78.267780 is in the general vicinity. It might be interesting to revisit this site to see if the same species is growing there 60 years on.)
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Mr. Godfrey collected two examples of this sedge. He made sure to collect some
noticeable roots on the larger specimen. In both cases, the structure of the plants’ bases
is visible, with several stalks growing in a clump. Both plants were in flower at the time
of collection – this is standard practice in herbarium collection, because many plants are
difficult to identify without their flowers. The specimens are affixed to the page with
strips of linen paper, quite similar to that used in the older specimen.
Flower, roots, and linen strips
[ link to interactive view ]
4. Magnolia
This specimen is from a
Magnolia insignis Wall. growing in the South Carolina Botanical
Garden at Clemson University. The herbarium curator, Dixie Damrel, prepared this specimen
as part of the data that the botanical garden records on its living collections. She
collected this specimen in May, 2010, proof that herbarium work is still relevant.
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These leaves came from the plant identified by accession number 990849. (The
number on the specimen's label contains a typographical error, an extra zero, identifying the plant as "9900849".)
The accession tag on the living plant, showing the correct ID number.
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The label notes that
this species was formerly known as
Manglieta insignis, but that the current generic name
is
Magnolia. Below the scientific name is the common name. Scientists avoid using common
names to identify plants because there is no consistency among them, but common names can
also be useful or interesting to visitors so gardens keep track of them. This label
contains a detailed description of the plant’s appearance and origin.
Ms. Damrel has taken advantage of modern photography to enhance this specimen, including
a color photograph of a blossom. The plant may not have been in bloom when she visited it, which would have made it impossible to include a pressed flower. The photograph is in some ways better than a pressed dried flower; color is much easier to see. On the other hand, a photograph cannot convey the texture of the petals and reproductive structures, and certainly would not contain usable DNA or seeds. (See, e.g. Godefroid et
al. 2011, Lehtonen and Christenhusz
2010).
Note the stamps in the upper left hand corner of the herbarium speciment. “Voucher, not for exchange,” means that
this specimen is the one that the Clemson herbarium uses to identify this particular
plant, and that they will not share it with other institutions or scholars who wish to
study this species in particular or magnolias in general. The specimen is number 86861 in
the herbarium’s collection. The plant is a cultivated plant, as opposed to a plant
collected from the wild.
“Voucher” identification on the herbarium specimen
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The label describes the plant’s location in very precise detail, including GPS
coordinates. This makes it very easy to locate the plant in the garden’s collections,
either using the verbal description while exploring on foot or using the GPS coordinates
on an electronic device. And in fact, this plant is indeed alive and well and flourishing in the garden, as shown by these photographs taken on 2 May 2011, one years after Ms. Damrel made the specimen.
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