Close-up View of the "Pincushion Protea"
by Brian Johnston (Canada)
extraordinary it must be to live in South Africa, and be able to look
out the window to see Pincushion Protea bushes in full bloom.
These brilliantly coloured flowers are striking, not only because of
their appearance, but also for their unusual structure and pollination
sequence. In Canada, where I live, the plant is available only as
a cut-flower which is used in the making of elaborate floral
All members of the Protea family
are woody shrubs or trees. The leaves, which can be seen in the
image above, are hard and leathery (sclerophyllous).
The worldwide popularity of the Proteas has resulted in many hybrids
and cultivars being produced to supply the cut-flower market.
Most are grown in nurseries in Israel, California and Australia.
The following image shows a
colourful bloom. What you are looking at appears to be a single
flower, but it is not! In fact, this is a composite bloom , made
up of many small flowers and colourful bracts
(modified leaves). The bright orange-red stalks that emanate from
the flower-head, (the pins in the pincushion), are actually the pistils of individual flowers.
Each stalk consists of an orange column called the style, which supports a bright red
pointed stigma (the female
organ of the flower). (In this plant the pistil’s function is more
complicated than normal. This will be discussed later in the
The photographs that follow show
the flower-head from different points of view.
At the base of the flower-head,
there are multiple rings of purple-tipped green bracts. In the
right-hand image, the fine white hairs covering each bract are visible.
A much higher magnification reveals
each bract’s hairiness more clearly.
Notice, in the three images that
follow, the bright red ribbons that are associated with each pistil
column. If you look closely, you will see that each ribbon is
formed from four abutting narrower ribbons. These are the
specialized petals (called tepals)
that add much of the colour to the flower-head. The tepals are
intensely hairy on their undersides, and it is these white hairs that
provide the white background for the contents of the flower-head when
looking from a distance.
Before a flower “blooms”, the
pistil is curved, and the stigma end is buried back within the bundle
of tepals. As the bud opens, the tepals curl back to expose the
Proteas have distinctive male
reproductive organs (stamens).
The pollen producing anthers
do not have long supporting stalks (filaments),
as they do in many other flowers. Instead, they are joined
directly to the topmost portion of the ends of the tepals. One
such yellow anther can be seen in the bottom right corner of the image
below. The tip of the anther is framed by the curved end of the
When looking a the entire
flower-head, it is impossible to distinguish a single Protea
flower. Although difficult, it is possible to dissect one flower
from the head. A single such flower can be seen in the two images
that follow. The ovary, (in
which the seeds develop), is below the area shown in the photographs.
The labelled image below will be
used in the explanation of the pollination process in the Pincushion
Protea. (The perianths labelled in the diagram will be discussed
Protea flowers normally remain
closed, (with the style curved, and the stigma within the mass of
tepals), until an insect, bird, or rodent disturbs the flower. At
that point, the flower snaps open, the style straightens and the stigma
is held some distance above the bloom. During this process, the
stigma rubs against the stamens, and pollen becomes stuck to it.
This implies that the Protea is self-pollinating. The assumption
is incorrect. Proteas are protandrous;
the male organs mature before the female ones. When the immature
stigma picks up pollen from the stamens, fertilization doesn’t
occur. The stigma simply serves as an organ of pollen transfer,
and is therefore called the “pollen
presenter”. A few hours after being exposed to the air,
the pollen falls from the structure. From 24 to 36 hours after
the flower blooms, grooves (called stigmatic
grooves) open in the tip of the stigma which can accept pollen
from another plant. Fertilization can then occur.
The two images below show pollen
presenters. On the left, the curved styles indicate newly opened
flowers which can be seen to have some pollen attached to their
immature stigmas. On the right, older, straighter pollen
presenters are free of pollen.
Images of newly straightened pollen
presenters with their immature stigmas can be seen below.
A day later, similar stigmas are
Front and back views of the strange
structure holding the stamens of a flower can be seen below. The
sepals and petals, referred to as tepals, form the perianth. (Literally – “around the
anthers”.) The four perianth segments can be seen in the
images. While in bud, these segments abut one another, but don’t
overlap. As the bud blooms, the segments separate at the ends,
and curl back to expose the pollen presenter. The image on the
left shows three yellow anthers at the tips of perianth segments.
(If you look back to the labelled diagram of a flower, you can see that
one segment of the perianth, with its stamen, becomes coiled back, and
remains attached to the base of the flower. The other three
segments are unattached at the ends.)
A microscope allows a closer look
at the fine hairs attached to one side of a perianth segment.
Three images follow, showing the
anthers of Protea flowers. The last image reveals a single anther
with its protecting perianth segment tip.
A microscopic view of an anther,
separated from its perianth segment, can be seen below.
Under much higher magnification,
the tip of the perianth segment is covered with tiny, short, curved
Higher magnification of an anther
reveals pollen grains clinging to its surface.
combined with a higher magnification, shows individual Protea pollen
grains. The “auto-level”
function in Photoshop was used
to increase contrast in the right-hand image.
It is not only the flowers of the
Pincushion Protea plant that are unusual. Take a look, below, at
the tip of one of the plant’s leaves!
In their natural South African
habitat, the seeds produced by the Pincushion Protea are gathered up by
ants and buried in the soil. Only after a fire has killed the
overgrowing plants, and returned their nutrients to the soil, do the
seeds germinate to produce more of these spectacular blooms!
The photographs in the article were
taken with an eight megapixel Sony CyberShot DSC-F828 equipped with
achromatic close-up lenses (Nikon 5T, 6T, Sony VCL-M3358, and shorter
focal length achromat) used singly or in combination. The lenses screw
into the 58 mm filter threads of the camera lens. (These produce
a magnification of from 0.5X to 10X for a 4x6 inch image.) Still
higher magnifications were obtained by using a macro coupler (which has
two male threads) to attach a reversed
50 mm focal length f 1.4 Olympus
SLR lens to the F828. (The magnification here is about 14X for a
4x6 inch image.) The photomicrographs were taken with a Leitz SM-Pol
microscope (using a dark ground condenser), and the Coolpix
Pollination of Proteas:
Microscopy UK or their contributors.
Published in the
December 2005 edition of Micscape.
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