Close-up View of a Blooming Cactus
Family - Cactaceae
by Brian Johnston (Canada)
The distinctive appearance of cacti has
made them popular as houseplants, and where conditions are
ornamental landscaping plants. Since most are native to
hot, dry regions of the Americas, they have developed many
strategies to enhance their chances of survival under these
inhospitable conditions. Cacti are succulents (succus
‘leaf’), and store water in their stems. Since most
no leaves in the normal sense, these having evolved into their
characteristic spines, their stems have become photosynthetic,
evidenced by their green colouration. In order to minimize
loss from the stem’s surface, the ideal shape is a sphere, which
the lowest surface area for a given volume. Most cacti are
reasonably close to this ideal, with spherical, barrel-like, or
candle-like forms commonly being observed.
While searching for a subject
Micscape article at my local greenhouse, I came upon the cactus
below. Since this plant was in the process of blooming, it
like an ideal choice. Approximately 15 centimetres in
flowers had diameters of a little over a centimetre. The
was unlabelled, and since cacti are notoriously difficult to
I will simply describe it as a typical example.
The main plant is roughly
shaped, and near its base are rings of much smaller, almost
At the tip of this main plant
several flowers in full bloom. Each is radially
contains both male and female reproductive structures. Its
are shiny, and the lighter highlights are visible in the image
The images below show many
in the blooming process. Later we will see these stages in
As can be seen below, the
of the cactus is covered with a variety of spines. Each
spines grows from a bump on the surface called a tubercle. Each
an areole, a patch of
from which spines are propagated. (In the plant world,
are found only in cacti.) These spines protect the plant
predators, and they also help to channel dew, condensed from
air, down the stem to the plant’s roots. If you look
the following images, you will see that there are two different
spines arising from each tubercle. First, two red-brown
project from the tubercle’s centre forming a ‘V’ shape above its
surface. These two spines are referred to as the ‘central group’. Closer
plant’s surface is the ‘radial
flexible white spines grow radially around the circumference
of the areole’s apex. The white colour of these radial
thought to partially protect the plant’s surface from the sun’s
A still closer view shows the
of an areole, and both its central and radial groups of
Notice at the point of connection of the two red-brown central
that there is a very small patch of bright white fibrous
material. (In some cactus species this patch is much
size, and contributes much more to the ultra-violet filtration
Each cactus areole is formed
sections, an upper and a lower. From the upper section,
bud or a side shoot may form. The lower section is where
spines are found. In the image below, a bud has projected
areole’s upper section. As it increases in size it must
aside the flexible radial spines blocking its path.
Two unusually shaped buds with
depressed tips can be seen in the images that follow.
Images showing typically
buds growing up through the maze of spines on the plant’s
be seen below.
Notice in this image that the
bright red petals of the bud are surrounded, and protected by a
light pink, rounded sepals or bracts.
Some of the enlarging buds
bright red colour (first image), while others are much lighter
Closer views of a bud about to
bloom reveal its strikingly beautiful structure and colouration.
As buds begin to open, the
prominent, bright yellow pistils that project from their bases
While taking photomicrographs
the light coloured base of one of the sepals surrounding a bud,
noticed movement through the microscope. Closer inspection
revealed the presence of an extremely tiny sucking insect on the
sepal’s outer surface.
Notice the overlapping rings
petals that form the flower’s corolla. Each petal has a
longitudinal strip along its centre line.
In the images that follow,
many pale yellow male stamens that cluster at the base of a
These reproductive structures
be seen more clearly in the image below. Notice also the
of the flower’s petals.
The photomicrographs that
show the rectangular cells that create the petal’s structure.
Photomicrographs showing the
colourful outer sections of a petal reveal similarly shaped
Each male stamen is composed
white, hair-like supporting filament,
yellow, pollen encrusted anther.
The first two images below
roughly spherical pollen grains on an anther’s surface.
image shows similar pollen grains clinging to the surface of the
filament. Notice that each pollen grain appears to be bisected
A sequence of images showing a
flower’s five-lobbed stigma, taken with increasing
be seen below. The observer is close enough in the last
be able to distinguish the small lobes that cover its surface.
Photomicrographs of a stigma
which show these lobes even more clearly. The lobes
stigma’s surface area, and thus improve its ability to capture
retain pollen grains deposited by wind, insects or birds.
these pollen grains are clearly visible in the images.
Although most cacti are
to be ornamental plants, there are some that have commercial
uses. The fruit of the prickly pear and Hylocereus (Dragon fruit)
edible, and many farmers in suitable regions grow such plants as
crops. The Opuntia cactus
the host for cochineal bugs in the cochineal dye industry in
Central America. Although the cactus studied in this
no such important uses, it can be valued highly simply for its
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
January 2013 edition of Micscape.
Please report any Web
offer general comments to the Micscape
Micscape is the on-line monthly
of the Microscopy UK web
site at Microscopy-UK
Onview.net Ltd, Microscopy-UK, and all contributors 1995
rights reserved. Main site is at www.microscopy-uk.org.uk
with full mirror at www.microscopy-uk.net .