BSA's Classroom Plant Talking Point
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Interesting Jobs - Crime Scene Botanicals - Forensic Botany
(excerpt from the Plant Science Bulletin 52-3)
Early in January, 1935, a man named Arthur Koehler
worked his way through crowds of people gathered
outside the courthouse in Flemington, New Jersey.
He was there to testify in one of the most important
trials of the 20th century, the trial of Bruno Richard
Hauptmann for the kidnapping of the young son of
aviation hero Charles Lindbergh and his wife Anne.
Dr. Koehler was an expert on wood anatomy and
identification at the Forest Products Laboratory,
United States Forest Service in Madison, Wisconsin
and what was unique about the particular testimony
he was about to give was that it dealt with the
structure of wood, namely the wood of the ladder
used by the kidnapper. Presenting that kind of
evidence was highly unusual, there was little
precedence for it, and it was not clear it would even
be allowed. The use of scientific expert witnesses
was an uncommon and limited practice at that time
and botanical evidence had little standing in the
The defense argued strongly against allowing Dr.
Koehler to testify, saying “there is no such animal
known among men as an expert on wood; that it is
not a science that has been recognized by the
courts; that it is not in a class with handwriting experts, with fingerprint experts, or with ballistic
experts... The witness probably may testify as an
experienced carpenter or something like that, ….
but when it comes to expessing an opinion as an
expert or as a scientist, why that is quite different
indeed. We say that the opinion of the jurors is just
as good...” (Pope 1935). The judge responded, in
what we can now consider to be an historical
moment for forensic plant science, “I deam [sic] this
witness to be qualified as an expert” (Trenchard 1935).
Koehler subsequently went on in the trial to
demonstrate how the wood of the ladder, beyond
any doubt, linked Hauptmann directly to the crime.
The ladder was a unique design, homemade, and
in 3 parts that could be disassembled to fit in a car.
Koehler presented three kinds of information from
his study of the ladder - 1) identification of the wood
used, 2) physical marks left by tools on the wood,
and 3) comparisons of the wood structure. He was
able to determine that the wood used in the ladder
was of four kinds: douglas fir (Pseudotsuga
menziesii (Mirb.) Franco), 2 types of pine (Pinus
ponderosa Dougl. ex Laws. and Pinus echinata Mill., or a close species, commonly called yellow
pine) and birch (Betula sp., probably B. alba L.)
used for the connecting dowels. In making the
identifications he saw the characteristic presence
in pine of very thin epithelial cells lining the resin
canals, while in douglas fir he distinguished
characteristic thick-walled cells lining the canals
and faint spiral markings along the length of the
tracheids (Fig. 1). The wood of the top left rail had
clearly been used before. It had been sawn away
from a bigger piece and there were nail holes
present made by old-fashioned square-headed
nails. Koehler alerted authorities to look for a
missing board in any place connected with a future
suspect. Remarkably, Koehler using scarcely
visible planer markings was able to trace the some
of the pine back to its original mill source in
McCormick, South Carolina and then forward to the National Lumber and Millwork Co. in the Bronx, NY
just 10 blocks from Hauptmann’s home. This was
prior to Hauptmann’s arrest after passing a bill from
the ransom money. A week after the arrest, police
realized that one of the floor boards in Hauptmann’s
attic had been partly cut away. Koehler was able to
show in the trial that the attic board and the ladder rail had once been a single board by the exact match
of annual rings (Fig. 2) and importantly, he
demonstrated that patterns of annual rings are
unique so that no other random board would have
an absolutely identical pattern, just as today we
demonstrate that portions of our DNA are unique to
each individual. The wood anatomical evidence ultimately was one of the most incriminating and
unshakable pieces of evidence that led to
Hauptmann’s conviction and eventual electrocution
for the kidnapping (Graham, S. 1997).
Since that trial, what is termed forensic botany, or
the use of plant remains to help solve crimes or
other legal problems, has been widely accepted as
valid scientific evidence by the courts. If the wildly
popular televison crime shows like CSI, Law and
Order, Cold Case, and many others reflect to some
degree how real life detective work proceeds, then
plants are now beginning to play an increasing role
in solving crimes. In February this year in a TV
episode of “Bones”, one of the forensic
anthropologists finds part of an ear bitten off the
killer of a young woman. On the ear is ear wax within
which pollen is embedded. As the story continues,
the pollen is identified as a species of the grass
genus Eragrostis, a species said to grow only in
South Africa, and this leads the scientists to a
suspect who has just come from there. I comment
further on this story later, but the point here is that
although this particular case is fiction, plants or
parts of plants can provide significant supporting,
sometimes, crucial evidence in solving crimes.
The reasons for this are several: 1) plant remains
can be found almost everywhere; 2) they offer
multiple sources of evidence, both macroscopic
and microscopic, such as pieces of wood, (even as
charcoal), seeds, fruits, leaves, twigs, plant hairs,
microscopic air-borne pollen and spores, or in
aquatic environments, algal cells; 3) their
morphological diversity allows us to identify them
and from the identification gather other useful
information such as the season or geographical
location in which a crime took place, whether a body has been moved following a murder; if a body is
buried, how long it has been buried, and whether a
suspect was present at the crime scene.
Pollen and spores, in particular, have all the useful
characters just mentioned. Being widespread in
nature in the air and on most surfaces, we breathe
them into our lungs and they stick to our clothes.
Pollen and spore exines are amazingly diverse,
sometimes even to the species level, and their
production is generally seasonally and often
geographically restricted, thus their presence can
point to a specific season, sometimes even a
specific location, in which a crime was committed
(Szibor, R. et al. 1998). There are many published
examples of pollen morphology among related
families or within families or genera that illustrate
this diversity and consequently their usefulness as
trace evidence (e.g. Nowicke and Skvarla 1977, Caryophyllales;
Graham, A. and Barker 1981, Fabaceae, Caesalpinioideae;
Patel et al. 1984, Myrtales; Bruce and Dettmann 1996; Fig. 3). In
addition, they have other advantages. They are slow
to decay; pollen can be retrieved from rocks millions
of years old, a valuable asset for oil companies and
archeologists. Because they are microscopic, they
remain unseen, silent witnesses and even if they
were visible, unlike fingerprints, they would be
nearly impossible to eliminate from a crime scene.
A recent example from New Zealand illustrates how
pollen as trace evidence was used to solve a crime
(Mildenhall 1998). In Christchurch in 1997, a young
woman was grabbed, pulled into an alleyway, and
raped. Although shaken, she was able to describe
the assailant and shortly after a man matching her
description was arrested. The suspect admitted
being in the area and noticing this woman, who
seemed a little distressed, he said he stopped to
ask her if she was OK. Now, he claimed, she must
be putting his face on the face of the rapist, because
he had not been in the alleyway. There was no DNA
evidence, but the police noted dirt-stains on his
clothes. These, he said, came from his yard where
he was working on his car.
The alleyway where the crime occurred was lined
along one side by a row of low flowering shrubs of
wormwood, Artemisia arborescens L. a
Mediterranean native. The shrubs had been broken
and flattened during the struggle that led up to the
rape. The suspect’s clothes with the dirt stains were
sent for analysis together with a comparative sample
of soil from the crime scene to the forensic palynology
laboratory of the New Zealand Geological Survey.
The soil sample was dominated, as might be
expected by pollen of Artemisia (77%), much of it
occurring in clumps, indicating the source was at
the scene and had not merely blown in. The pollen
of this genus has a distinctive, echinate (spiny), very thick-walled exine. There was a mix of mix of fresh
pollen and somewhat older, darker colored grains,
as well as an unusual large, thick-walled fungal
spore in the soil sample, and other spore and
pollen types in very low percentages. The same
Artemisia pollen dominated the clothing sample
(53%), again occurring mainly in clumps, in a mix of
fresh and older grains, and the same thick-walled
fungal spore type was abundant. The percentage
of Artemisia was so high that the only explanation
was that the clothing was in direct, forceful contact
with an Artemisia plant. Investigators searched for
wormwood near the suspect’s home, and other
places he visited but found none. The species is not
common in New Zealand, being only occasionally
planted in gardens. The forensic laboratory had
processed over 1000 pollen samples from many
localities in New Zealand and never found Artemisia in more than a trace amount, so the chances of
finding large amounts were statistically 1 in 1000,
but in actual fact, chances were certainly much
lower. The fungal spores were also rare. This
pollen and spore evidence was presented at the
trial, the suspect was convicted, and was given an
8 year prison sentence. Similar comparative pollen
evidence led to conviction of a murder suspect in
northern Australia (Milne 2005), and in a civil case
where pollen intake to a gasoline line was cited as
the cause of a fatal plane crash, pollen provided
important evidence negating the claim (Graham, A. 1997).
Returning to the use of plants in crime TV shows,
and specifically the finding of Eragrostis grass
pollen in ear wax that led to a suspect, the science
of this story presents a bit of a problem. Although
many plant groups have spectacular pollen
morphology, not all pollen is remarkable structurally
and sadly the pollen of grasses, one of the most
common and widespread plant families in the
world, is nearly as feature-less as a ping-pong ball,
so it would have been impossible to identify an Eragrostis plant to genus or species and pinpoint
the geographical source based on pollen (Fig. 4).
An interesting exception in the pollen of grasses is
cultivated corn which has extremely large pollen, ca.
100um in diameter, compared with a more average
pollen diameter of ca. 35um..
Seeds and fruits, like pollen, very often give away
their identity by their specialized features, especially
if they are provided with hooks or barbs. These
structures have evolved to aid in dispersing progeny
away from competition with the parent plant and are
very effective in their role, as anyone who has
walked through a field in summer or fall has
experienced. In 1997 in Ohio, I was called by the
sheriff’s department of Champaign Co. near
Columbus, Ohio to identify some seeds (actually single-seeded fruits) associated with the murder of
two children. The children were found buried in an
area at the shady wooded margin of a local cemetery
not long after they were reported missing by the
stepfather. He soon became a suspect. I identified
the seeds as from Geum canadense Jacq. (or
possibly Geum aleppicum Jacq. with very similar
fruits), commonly known as avens, in the Rosaceae
and from Galium aparine L., bedstraw, in the
Rubiaceae, species of shaded to partly sunny places
in dry to moist somewhat disturbed woodlands
(Fig. 5). The seeds had been removed from a
blanket and the stepfather’s clothing recovered at
his house. He claimed the seeds came from his
small farmyard, but neither plant occurred in his
open weedy yard, nor would they have been expected
there. Both species were found at the gravesite. The
seed evidence linked the suspect to a wooded area
such as that of the gravesite and was part of the
evidence introduced at the trial (State of Ohio vs.
Kevin Neal, 2000). He was convicted of the two murders and is now serving two life sentences.
Similar investigations employing seed evidence
from crime scenes have been reported by Lipscomb
and Diggs (1998) and in a case investigated by
David Hall, summarized at www.nwf.org/wildlife/ wildlifecrime.cfm.
Botanical trace evidence is also obtained from plant
cells found in gastric contents. Many of the common
foods we eat contain seeds or other plant parts with
specialized cells having thick walls of cellulose and
lignin. Because these materials do not digest or
digest only slowly they can be present in partially
digested stomach contents or excreted in feces,
and are often able to be identified in degraded form
(Bock, J. H. et al. 1988). It is sometimes possible
to determine components of a victim’s last meal
which, in turn, can provide clues to the setting or
timing of death. In a particularly tragic case in
London in 2001, partially digested plant material
even gave a clue to the victim’s homeland and
suggested a reason for his death.
The case began in September, 2001, when the
torso, minus limbs and head, of a young boy 4-7
years in age was found in the Thames River. There
was little to use for identification based on standard techniques and there were no corresponding
missing child reports. Scotland Yard suspected
from the condition of the body, which had been
deliberately drained of blood, that they might be
dealing with a ritual killing – a human sacrifice. They
turned to forensic scientists, including a palynologist
and a plant anatomist to look for whatever evidence
might give them a lead in the case. DNA suggested
the child was West African in origin and the contents
of the digestive tract revealed alder (Alnus) pollen,
a tree native to northern Europe, and was an
indication that the child had been in England in the
days prior to his death.
Of greatest interest was the presence in the stomach
and intestines of an unusual assortment of small
mineral pieces, clay pellets embedded with minute
gold particles, and the remains of some type of
bean seed. The anatomy of seeds in some plant
families, including the legumes (Fabaceae), the
mustards (Brassicaceae), and the tomato-potato
family (Solanaceae), is quite distinctive and can
even be species-specific in some taxa. By comparing
seed coat anatomy from the stomach contents of
the boy, the seeds were closely matched by a plant
anatomist at the Royal Botanical Gardens in Kew to
a highly poisonous legume from West Africa, the
Calabar bean (Physostigma venenosum Balf.).
Anatomical recognition of legume seeds is possible
because the outermost cells of the seed coat consist
of a diagnostic palisade layer in which the cells are
typically narrow, elongate, and very thick-walled. It is
the heavy walls that make them resistant to quick
dissolution. The next deeper layer also can be quite
diverse and help in narrowing an identification. The
presence of Calabar beans in this case, mixed with
the other unusual items in the stomach, suggested
the child had been given a toxic paralytic voodoo
potion. This finding pointed, like the DNA, to areas
of West Africa, like Nigeria, where witchcraft is
known to be practised still, and it supported the idea
that the child had been a human sacrifice.
Further investigations, using bone chemistry,
narrowed the home of the boy to an area near Benin,
Nigeria, where Calabar bean is native and where
animal, and rarely human, sacrifice is performed. Thus far, no one has been arrested for the murder
but as part of the investigation, a ring trafficking in
people from Africa into Great Britain and Germany
was uncovered and shut-down and 21 people
involved were arrested, including the man who
brought the child from Africa (The Guardian 2004;
see also National Geographic Channel
presentation, “The Witchcraft Murder”, 13 Feb 2005).
Today the fastest growing component of botanical
evidence in forensics is molecular evidence. We
are in early stages of this type of plant trace evidence.
The first instance in which data from plant DNA was
accepted as admissible evidence in a criminal case was in Arizona in 1992. In that case, State of
Arizona vs. Bogan, a young woman was murdered
and her body dumped in the desert. The suspect
was taken into custody after his pager was found
near the site. He claimed he had given the woman
a ride and that she had stolen his wallet and pager
from his truck. A member of the Maricopa Co.
investigating team, Charles Norton, happened to
notice that one of the palo verde trees (Parkinsonia
microphylla Torr.) at the scene was freshly scraped,
possibly by the murder’s vehicle. On an impulse he
picked some seed pods hanging from the tree;
later, the same kind of pods were found loose in the
open truck bed of Bogan’s truck and Norton, knowing
that DNA could identify human individuals, thought
perhaps the pods could be linked by their DNA to the
tree at the crime scene. Dr. Tim Helentjaris, a
geneticist at the University of Arizona agreed to try.
Using RAPDs (Randomly Amplified Polymorphic
DNA) to produce profiles of visualized DNA
fragments- a kind of ‘fingerprint’ of individuals
being studied, he was able to match the DNA from
the 2 seed pods found in the truck to the seed pods
collected from the tree at the scene and only to that
tree. This was because the palo verde trees had an
exceptionally high degree of intraspecific genetic
variation (Yoon 1993). The truck, if not the suspect,
had definitely been at the site. The jurors agreed
Helentjaris’s findings were very influential in their
decision to find Bogan guilty of first degree murder.
In recent plant DNA research, botanists at the
Australian National University in Canberra, Australia
have produced a prototype identification system for
grasses based on DNA, a kind of molecular
taxonomic key (Ward et al. 2004). Although grass
pollen is not generally helpful in forensics, other
parts of grasses like seeds and stem or leaf
fragments can be a good source of DNA and
because grasses are among the most likely plants
to be encountered as trace evidence, a means of
identification would be a valuable tool. In their study,
using primers designed for the purpose, they
sequenced parts of the mitochondrial genome that
were representative of subfamily, tribe and genus
ranks within a test set of 20 samples. These were
then used to identify 25 unknown grass samples in
a blind test. With more complete representation,
the possibility of identification of many more kinds
of grasses by molecular means seems to be within
It is unfortunate that in this country, botanical trace
evidence is still poorly integrated into crime scene
analyses, in spite of its potential in many situations.
In 1990, a survey of 30 of the largest forensic
laboratories in the United States found that only 2
knew pollen could be used as a forensic tool (Bryant and Mildenhall 1990). This figure has not risen
significantly in the past 16 years even though criminal investigations are becoming more
sophisticated in treating other aspects of trace
evidence (Bryant and Jones in press).
In great part, the failure to incorporate botanical
evidence in investigations is due to lack of
knowledge about plants by personnel who study
crime scenes and so fail to collect it. The FBI’s 2003
Handbook of Forensic Services (www.fbi.gov)
mentions the usefulness of wood and cotton fibers
and explains how these should be submitted for
examination, but refers to no other kind of supporting
plant evidence. Unless plant parts are
conspicuously evident, samples of plant materials
are not standardly taken, nor are specialists brought
in to record critical observations of vegetation that
could yield credible evidence.
The assessment of plant evidence requires welltrained
specialists and frequently also access to
extensive reference collections. Today, specialists
in plant systematics, plant anatomy and morphology,
and palynology are relatively few in number, and
aging, and younger replacements are increasingly
rare. The balance in plant science research has
tipped so heavily toward molecular-based research
that students interested in whole plant-based
studies find fewer and fewer relevant botany courses
available at universities, little research support at
the graduate level, and few job opportunities. The
value of botanical trace evidence in criminal and civil
cases has been clearly demonstrated and is
accepted by the courts. Justice can now only be
more fully served when law enforcement agencies
and other relevant groups recognize and take full
advantage of its utility and open employment
opportunities for botanically trained investigators.
Academic institutions, for their part, must once
more appreciate the value of providing well-rounded
instruction in botany within their undergraduate
Bock, J. H., M. A. Lane, D. O. Norris. 1988. Identifying Plant
Food Cells in Gastric Contents for Use in Forensic
Investigations: A Laboratory Manual. U. S. Dept. of Justice,
National Institute of Justice Research Report, January
Bruce, R. G. and M. E. Dettmann. 1996. Palynological
analyses of Australian surface soils and their potential in
forensic science. Forensic Science International 81: 77-
Bryant, V. M., Jr. and G. D. Jones. 2006. Forensic
palynology: current status of a rarely used technique in the
United States of America. Forensic Science International:
Bryant, V. M., Jr. and D. C. Mildenhall. 1990. Forensic
palynology in the United States of America. Palynology 14:
Graham, A. 1997. Forensic palynology and the Ruidoso,
New Mexico plane crash – the pollen evidence II. In:
Graham, A. Symposium Ed., Forensic Chemistry, Soil
Analysis, Entomology, Botany, Palynology, and other
Aspects of Non-genetic-marker Biology. Journal of
Forensic Sciences 42: 391-393.
Graham, A. and G. Barker. 1981. Palynology and tribal
classification in the Caesalpinioideae, Pp 801-834 in: R.
M. Polhill and Peter Raven, Eds., Advances in Legume
Systematics. HMSO, London.
Graham, S. 1997. Anatomy of the Lindbergh kidnapping.
Journal of Forensic Sciences 42: 368-377.
Lipscomb, B. L. and G. M. Diggs, Jr. 1998. The use of
animal-dispersed seeds and fruits in forensic botany.
SIDA 18: 335-346.
Mildenhall, D. 1998. It takes just a few specks of dust and
you are caught. Canadian Association of Palynologists
Newsletter 21: 18-21.
Milne, Lynn. 2005. A Grain of Truth. How Pollen Brought
a Murderer to Justice. Reed New Holland Publ., Sydney,
The Guardian. 2004. Jail for torso case people smuggler.
27 Jul 2004. United Kingdom.
Nowicke, J. W. and J. J. Skvarla. 1977. Pollen morphology
and the relationship of the Plumbaginaceae, Polygonaceae,
and Primulaceae to the order Centrospermae. Smithsonian
Contributions to Botany 37: 1-64.
Patel, V. C., J. J. Skvarla, and P. H. Raven. 1984. Pollen
characters in relation to the delimitation of Myrtales. Ann.
Missouri Bot. Gard. 71: 858-969.
Pope, F. State of New Jersey vs. Bruno Richard
Hauptmann, Trial transcript, 1935: 3796.
Szibor, R., C. Schubert, R. Schöning, D. Krause, and U.
Wendt. 1998. Pollen analysis reveals murder season.
Nature 395: 449-450.
Trenchard, T. W. State of New Jersey vs. Bruno Richard
Hauptmann, Trial transcript, 1935: 3805.
Ward, J., R. Peakall, S. R. Gilmore, and J. Robertson. 2005.
A molecular identification system for grasses: a novel
technology for forensic botany. Forensic Science
International 152: 121-131.
Yoon, C. K. 1993. Botanical witness for the prosecution.
Science 260: 894-895.
Thanks for stopping by!!
The information contained in this "Plant
Talking Point" was supplied by Dr. Shirley Graham,
Missouri Botanical Garden, and is BSA