A close up of the golden tower spurge
Close-up View of the
'Golden Tower' Spurge
by Brian Johnston (Canada)
Spurges, members of the Euphorbiaceae family,
unusual trait; they have ‘naked flowers’ which are missing
petals, but which possess a whorl of (sometimes) colourful
Euphorbias are extremely
they can be small and grass-like, or huge trees. The Euphorbia
has approximately 300 genera, and 5000 species. Genus Euphorbia alone contains
2000 species. Some of the plants are of economic importance. The
manioc, caster bean, and para rubber tree are examples. Some,
the crown of thorns (Euphorbia
hybrids), and the African milk tree (Euphorbia
trigona), are grown as ornamental plants.
One important characteristic
euphorbias that should be kept in mind, is that they exude a
called a phytotoxin from cut leaves and stems that is poisonous,
corrosive to skin and eyes. The phytotoxins produced by
contain diterpene esters, alkaloids, glycosides and ricin-type
The severity of the symptoms depends on the particular species
name, comes from a Greek surgeon named Euphorbus, who, it is said, used
the milky sap of the plants in his curative potions!
The particular hybrid studied
this article is the Golden Tower Spurge, Euphorbia cornigera ‘Goldener
Sometimes called the Himalayan Spurge, it possesses green leaves
distinctive white central vein, and numerous bright yellow-green
flower-heads. (The plant’s developer describes the colour
blooms as chartreuse-yellow.) This colour scheme can be
the first image in the article.
Although the plant’s
refers to its upright habit, the reality is that the stems are
extremely straggly, and often bend through extreme angles,
some of the flower-heads being level with the ground. This
problems when photographing the plant, and in some cases the
pot had to be supported 20 to 30 centimetres above the
table-top, in a
horizontal position, in order to obtain the required
Mature stems are red-brown in colour, while immature ones are
The number of oval
bracts surrounding the central flowers is usually three,
although as we
will see later, the number can be two, or even four. In
that follows, the actual flowers can be distinguished by their
orange-yellow structures. Second generation flower-heads,
their associated bracts grow from within the main flower-head.
As you can see in the three
that follow, leaves near the tip of the stalk tend to be much
green than those further down the stem. Usually leaves are
alternate positions along the stem, but there are some
The following group of images
the plant’s strikingly coloured flower-heads. It is not
surprising that the cultivar name “Golden Tower” was chosen for
Spurges possess a highly
specialized inflorescence (bloom), called the cyathium. This
is a cup-like cluster or whorl of bracts that encloses a group
structures including a single female (pistillate) flower, ringed
several male (staminate) flowers. Both the female and male
enclosed within a ring formed by five horseshoe shaped glands
(involucral glands). These glands secrete a shallow layer of
which is attractive to flies, and other insects. (The name
from the Latin kuathion,
diminutive of kuathos,
meaning “ladle”.) The two images below show an ‘old’
which the stalk holding the ovary and its attached pistil has
from vertical by more than ninety degrees. The male
shriveled and fallen from the flower, leaving behind the ring of
By contrast, most of the
visible in the image that follows are at a very early stage of
development. Here only a swelling at the centre denotes
presence of the ovary, and no pistil or stamens are
the involucral glands are a green rather than orange colour.
As the cyathium develops, the
begins to protrude from the ring of involucral glands, and the
three-lobed stigma extends from the top of the ovary.
In the two images below, the
stigma, style and bulbous green ovary (seed producing organ) of
female flower have bent away from their vertical position.
male (staminate) flowers have appeared, with bright yellow
their bi-lobed tips. Having a flower-head’s pistillate
appear much earlier than its staminate flowers tends to decrease
chance of self-fertilization. The stigma can receive
carried pollen from other plants before pollen grains from the
flower-head’s nearby male flowers become available. By
the female flower away from nearby male flowers, the possibility
reduced even more!
This image shows an
stage, just as the female flower starts to bend away in order to
room’ for the male flowers that are about to appear.
Even before the cyathium
blooming, another generation begins its development. In
the four images, a light green pointed ‘baby’ cyathium can be
growing from beneath the ring of involucral glands. The
‘baby’ cyathia is variable; three can be seen in the fourth
Images showing these second
generation cyathia can be seen below.
When the male staminate
first appear, their bi-lobed anthers are covered by pale green
membranes. These membranes eventually decompose to reveal
abundant pollen grains that cover the tips of the lobes.
As time passes, the male
begin to turn brown, and fall away from the cyathium. In
fourth image, the brown remnants of male flowers can be seen
ring of involucral glands.
Notice the very large number
pollen grains that adhere to each lobe of a male flower’s
To me, the most interesting
of development is the fully blooming one.
The two images that follow
clearly the bifurcated tips of each stigma lobe, and the
style. Notice the bulbous tip of each lobe, and the bumpy
of the female flower’s ovary.
Only two male flowers remain
cyathium shown below.
Eventually, all of the male
die and fall away, leaving only their coloured bases.
most of the images, that the bumpy ovary is divided into
In the final stage, even the
flower turns brown and falls away, leaving only the bases of the
flowers, and the ring of involucral glands.
Shortly after photographing
Golden Tower Spurge, my local greenhouse brought in another
hybrid spurge called Kalipso. It had the scientific name Euphorbia hybrida ‘Imprkalip’.
image that follows shows its appearance. Notice that this
cultivar has only four involucral glands, and that the glands
bright red in colour and have light green ‘tips’ that extend
Compared with the earlier
this one is smaller, and more compact, and has many more leaves.
Opening leaves tend to be
in colour, and have hints of red colouration.
Additional images showing
flowers and immature cyathia can be seen below.
As before, a female flower
possesses a pistil consisting of a style which supports a stigma
three bifurcated tips.
The most obvious structural
difference is the number, shape and colour of the involucral
glands. In the last couple of images, the sticky coating
nectar can be seen glistening on the surface of involucral
Unlike the other spurge
that I have studied, this one never develops male flowers.
produced by asexual reproduction involving terminal vegetative
Spurges are popular garden
but not for the typical reasons. Here it is primarily
interesting shapes and subtle colour variations that whet the
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.
An 10 megapixel Canon 40D
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
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
October 2012 edition of Micscape.
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