Castor Bean Plant
by Brian Johnston (Canada)
The castor bean plant is a very fast
grower. In one year it can reach a height of more than
metres, and each of its leaves can end up being one metre
There are at least two downsides to growing them however.
live in the Northern climes where temperatures drop to 0 degrees
Celsius, the plant will die.
If you allow the plant to
its flowers, and form seeds, these seeds are extraordinarily
– the most deadly on earth! They contain the toxin ricin,
of which can kill an adult (2 to 3 seeds). A single seed
enough ricin to kill a small child. Unfortunately the
shiny, spotted seeds are beautiful. Worse still, when the
containing the seeds breaks open, they are ejected with
force away from the plant where they may be picked up by human
passers-by or by animals. Some jurisdictions discourage
planting of Ricinus communis
for these reasons. Others recommend that the flowers be
so that seeds will not form.
In the back of your mind you
remember being given castor oil (produced from the seeds of the
as a child. No, your parents were not trying to dispose of
you! Procedures are undertaken in the production process
castor oil to prevent ricin from being included.
communis is a member of the Spurge family
is distantly related to the poinsettia, and the rubber
other members of the family, this plant has very unusual flowers
occur in clusters at the ends of some of the stems. The
monoecious is used to describe plants like this one which have
male and female flowers. In this case, the female flowers
always located above their male counterparts. In the first
in the article, and those that follow, the female flowers can be
identified by their reddish pistils. Male flowers are
by their clusters of beige stamens.
Castor bean leaves are
shaped, with from 5 to 11 pointed lobes.
Let’s look more closely at the
plant’s female, or pistillate flowers . There are no
sepals, and each flower consists of three feathery-appearing,
stigma lobes connected by short, or non-existent styles to a
three-compartment, spiny ovary.
Since a newly opened leaf is
in these images, notice in the two closer views below, that the
of the lobes are very irregular, covered with what appear to be
perhaps glandular ‘bumps’. Interestingly, mature leaves do
have these tiny ‘curls’ along their edges.
In the images that follow we
now close enough to see that beneath the reddish stigmas, there
masses of yellow-green spines. These spines cover the
the ovary connected to the base of the stigmas.
Just to the right of the
pistillate flower in the image on the left below is a female
about to bloom. Two pink lobes can be seen peeking out of
beige capsule from which it is erupting. The image on the
shows a more highly magnified view.
The surfaces of the stigmas of
species have projections that help to collect and retain pollen
grains. Usually they are microscopically small. Here
however, they are large enough that even macro-photographs
Photomicrographs of these
structures reveal their cellular structure and variable
Beneath the castor bean’s
flowers are many male, or staminate ones. Notice in the
that the anthers and their supporting filaments are initially
within droplet shaped, light beige containers formed by five
When the staminate flower
the tips of the 5 sepals separate to reveal masses of shiny,
anthers. Their packing is so tight, that their filaments
Views of a second staminate
can be seen below.
Once the sepal container
stamens and their lengthening filaments soon extend out to form
large, branched, shrub-like structure.
When first exposed, the
are white, and the anthers light beige.
Within hours however, exposure
the atmosphere causes both anthers and filaments to turn a
greenish-brown colour. Eventually, after several days,
darken to a light brown colour.
The process whereby an anther
releases its pollen is called dehiscing. In this species
bi-lobed anther opens rather like a woman’s purse, revealing the
These pollen grains are
ellipsoidal in shape.
Approximately a week has gone
since the last photographs were taken. During that time
ovaries at the base of the pistillate flowers have dramatically
increased in size and now have a diameter of about 1.5
centimetres. Approximately spherical in shape, they are
with what look like yellowish-green spikes with a sharp spine at
When the sepal ‘container’
opens in a pistillate flower, these spikes are much more tightly
packed, with most of their spines pointing towards the stigma
As the sepal ‘container’
disintegrate, the spikes begin to separate.
Photomicrographs showing the
a green spike with its sharp spine can be seen below.
In order to expose the
flower cluster for the purpose of photographing it, I had to
several leaves. As soon as this was done, tiny leaves near
base of the plant began to grow at an amazing rate.
Leaves grow from the
points of stems. At first, tiny ‘bumps’ appear at the
A short time later a ‘bump’
a short stalk with a tiny folded leaflet encased by thin
Notice in the above images
bamboo-like ring exists at each branch point along the
closer view of one of these rings can be seen below.
New leaves are lighter green
very glossy. They have variable numbers of deeply indented
Older leaves are much duller,
this allows their complex vein pattern to be more easily seen.
The oldest leaves on the plant
greyish-green. The prominent longitudinal vein can be seen
Leaves viewed from below
their intricate three-dimensional vein pattern.
Notice in the image that
the two light green structures at the base of a leaf.
believed to be glands which exude secretions attractive to
If a browsing herbivore happens upon the plant, the biting or
ants may discourage ingestion.
The undersides of
older leaves are flatter than younger ones, and they are lighter
Notice the saw-blade-like edge
the tip of one of the leaves. If you compare this image
ones above, you will see that there is considerable diversity in
decoration in the plant.
At the limits of
the cellular structure of leaves barely becomes visible.
Much higher magnification
photomicrographs reveal the tiny red spots that are present on
surface of a leaf’s primary vein.
The underside of a leaf is
with many oval stomata, and their associated guard cells.
structures control the entry and exit of gases into and out of
The castor bean plant produces
quantities of dust-like pollen. Each grain is ellipsoidal
Over a week has passed, and
terminal flowering cluster has transformed into a cluster of
spiny ovaries. Notice that the red pistillate flowers’
have begun to disintegrate, and fall away.
Later still, these ovaries
grown to almost 2.5 centimetres in diameter.
this point, I had to consign the plant to the garbage, as I was
on a holiday.
Castor oil makes up about half
castor bean’s mass. This oil is valued for industrial as
medicinal purposes. Most is used in producing lubricants
machinery, automobile engines, and liquid products like paints,
Ricin, on the other hand, is
probably best known for its involvement in the 1978 murder of a
Bulgarian dissident named Georgi Markov, who worked for the BBC
London. The actual deed was done by placing a 1 mm ricin
containing pellet in the tip of a modified umbrella, and
in the leg with it!
The low magnification, (to
macro-photographs were taken using a 13 megapixel Canon 5D full
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
A 10 megapixel Canon 40D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of
The photomicrographs were
using a Leitz SM-Pol microscope (using a dark ground condenser),
the Coolpix 4500.
A Flower Garden of
A complete graphical index of
of my flower articles can be found here.
The Colourful World
A complete graphical index of
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
September 2013 edition of Micscape.
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