View of the Corn Cob Euphorbia
View of the
Corn Cob Euphorbia
by Brian Johnston (Canada)
This plant can be summed up in a single
word – peculiar. If it were not in bloom, you might guess that it
is a cactus. It does have tubercles, (bumps or swellings),
aligned in vertical rows like an ear of corn, and what look like
spines. However, cacti have clear sap, while this plant exudes a
milky liquid. Certainly its flowers, seen in the image above, are
not at all like those of most cacti. What could it be? The
answer of course, is an Euphorbia.
The genus Euphorbia is enormous, with over
2000 species displaying astonishing variations. For example this
plant and the Poinsettia are both Euphorbia. Is that different
enough? The genus name refers to Euphorbus, Greek physician to
Juba II, the King of Mauritania. Mammillaris, the species name is
translated as having nipples or breasts, and this refers to the many
swellings on the surface of the club-shaped plant.
Near the top of the plant, there
are whorls of tiny leaf-like structures above the ring of blooming
flowers. Beneath the flowers are a few of these thick leaflets,
and some that have turned a bright red colour. Also near the top
of the plant are thin pink rod-like structures which eventually dry out
to form stiff brown cactus-like spines, although they are not sharply
The four images that follow show
views of the top of the plant. At its tip, there are several
whorls of green leaflets. Further down the column, these leaflets
grow from the centre of each tubercle, and many are bright red in
colour. Still further down, these leaflets have dried up, and
fallen from the plant. Some, but not all tubercles have a fleshy
pink, rod-like structure which is a modified flower spike.
Eventually these spikes lose their colour and dry to form grayish-brown
The relative positions of the small
leaflets and modified flower spikes can be seen in the two images that
follow. The leaflets grow from the exact centre of a tubercle,
while the modified flower spikes grow at the intersection point of two
tubercles. The closer view on the right shows the red tops of
modified flower spikes as they begin to grow out from between two
Spikes do not have a sharply
pointed tip, and some have microscopically small leaflets growing from
the column near its tip. Notice how neatly the tubercles fit
together over the surface of the column.
A Euphorbia flower, more correctly
called a cyathium, is positioned on top a stalk referred to as a
pedicel. There are no petals, although in the images below, one
might think that the five rounded orange-yellow structures might
be. These are actually the flower’s nectar producing glands
(nectaries). Protruding from the centre of these glands is the
single stigma which consists of three forked tips supported by a stubby
style. Since close examination failed to show any evidence of
stamens, I suspect that this species has male flowers on a separate
The two images that follow show a
whorl of red-edged greenish leaflet-like structures immediately beneath
the nectary glands. These are petal-like bracts called petaloid
The structures that make up a Euphorbia mammillaris flower can be
seen clearly below. Growing from the tubercle is the whorl of
petaloid appendages, from the middle of which the pedicel
emerges. The pedicel ends in the ring of nectary glands, from
which the flower’s style protrudes. The style branches into three
stigma lobes, each being forked. Newer flowers tend to be yellow,
while older ones tend toward orange.
At the centre of the ring of
nectary glands there is a flat red area surrounding the style.
This contrasting colour may be an adaptation to help guide insects to
Closer views of this red area show
that it is covered in fine white hairs. Broader red hairs can be
seen in the image on the right, growing up against the style.
Also note that the surface of nectary glands is dimpled.
After a period of time,
(approximately a week), the nectary glands begin to disintegrate,
leaving only the pistil and petaloid appendages.
Unlike the cactus, whose defensive
spines are present for its entire life, the Corn Cob Euphorbia’s spine
stand-ins, the modified flower spikes, turn brown and drop off after
several months. The tiny leaflets at the centres of tubercles
also fall off leaving distinctively shaped scars.
Both flower-spike and leaflet scars
can be seen in the image on the left below. On the right is the
clear evidence that the plant is a Euphorbia, and not a Cactus.
The following group of images show
the small leaflets of the plant from a variety of points of view.
Notice that a leaflet has a red, concave upper surface, and a yellow,
convex lower surface. The leaflet’s thickness is also unusual.
Newly emerged modified flower
spikes can be seen below. Each green spike can be seen to have a
number of extremely small leaf-like structures near its tip.
At a later stage, the spike has
grown longer, and has an increased diameter. The closer view on
the right shows clearly the tiny leaf structures at its tip.
My local greenhouse had a group of Euphorbia mammillaris plants for
sale the day that I paid a visit. Only one was in bloom.
Its alien-looking flowers prompted be to bring it home, and this
article is the result.
The low magnification, (to 1:1),
macro-photographs were taken using a 13 megapixel Canon 5D full frame
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
An 10 megapixel Canon 40D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon macro
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
September 2011 edition of Micscape.
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