A Close-up View of a Yellow Pincushion Protea
by Brian Johnston (Canada)
For an earlier Micscape
photographed a brilliant orange-red pincushion protea.
Recently, I found a similar, but not identical example that has a
yellow colour. Much of the text of this article is identical to
the earlier one, but differences have been noted.
How extraordinary it must be to live in South Africa, or Australia, 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
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 images show a pincushion protea 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 yellow stalks that emanate from the flower-head, (the pins in
the pincushion), are actually the pistils of individual flowers.
Each stalk consists of an yellow column called the style, which supports an identically
coloured 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
At the base of the flower-head, there are multiple rings of
black-tipped green bracts. In the right-hand image, the fine
white hairs covering each bract are visible.
A photomicrograph showing several of these hairs can be seen below.
It is not only the flowers of the Pincushion Protea plant that are
unusual. Take a look below, at the unusual shape of the plant’s
leaves! (It is strange that these leaves are completely different
in shape than those of the red plant in the earlier article.)
The photomicrograph that follows shows a stoma and associated guard
cells that control gas entry into the underside of the leaf.
Notice, in the two images that follow, the yellow ribbons that are
associated with each pistil column. Each of these ribbons is
formed from four abutting narrower ribbons. These are the
specialized petals (called tepals) that enclose the brown stamens that
are visible in the image on the right. The tepals are much less
hairy than those on the red pincushion protea. Before a flower
“blooms”, the pistil is curved, and the stigma end is buried back
within the bundle of tepals.
A cross-section through an entire flower-head reveals its unusual and
complex structure. Many individual flowers are tightly packed
together on the surface of the roughly egg-shaped base structure.
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 image that follows. The ovary, (in which the seeds
develop), is below the area shown in the photograph. The long
curved structure is the style that holds an enlarged stigma at its
tip. At the base of the style, several tepals curve up to the
roughly egg-shaped structure that encloses the flower’s stamens.
Front and side 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 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 to expose the stigma which is
buried within the cup formed by the segments. The third image
shows three orange-brown anthers at the tips of perianth segments.
A microscope allows a closer look at the fine hairs attached to a
An immature anther can be seen on the left below. On the right is
a mature anther with some adhering pollen grains.
The cellular structure of the lower portion of the anther can be seen
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 three images below show pollen presenters. The curved styles
indicate newly opened flowers that can be seen to have some pollen
adhering to their immature stigmas.
The following image shows the tip of the stigma, with its coating of
yellow-brown pollen grains.
At much higher magnifications, the curved triangular shape of each
pollen grain is visible.
Three types of illumination reveal the detail of a single pincushion
protea pollen grain. The first image uses dark-ground
illumination, the second transmitted light illumination, and the third
uses phase-contrast illumination. Note that the “auto-level”
function in Photoshop was used
to increase contrast in the phase-contrast image.
In their natural 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 unusual blooms!
Most of the macro-photographs were taken with an eight megapixel Canon
20D DSLR equipped with a Canon EF 100 mm f 2.8 Macro lens which focuses
to 1:1. A Canon 250D achromatic close-up lens was used to obtain
higher magnifications in several images.
A few photographs were taken with an eight megapixel Sony CyberShot
DSC-F 828 equipped with achromatic close-up lenses (Canon 250D, 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.
The photomicrographs were taken with a Leitz SM-Pol microscope (using
dark ground and phase-contrast condensers), and the Coolpix 4500.
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 August
2010 edition of Micscape.
Please report any Web problems or
offer general comments to the Micscape
Micscape is the on-line monthly magazine
of the Microscopy UK web
site at Microscopy-UK
Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All
rights reserved. Main site is at www.microscopy-uk.org.uk
with full mirror at www.microscopy-uk.net .