A Close-up View of the "Pincushion Protea"

(Leucospermum cordifolium)

by Brian Johnston   (Canada)

How 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 arrangements.

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 article.)

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 style.

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 red tepal.

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 later.)

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 pollen free.

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 hairs.

Higher magnification of an anther reveals pollen grains clinging to its surface.

Phase-contrast illumination, 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!

Photographic Equipment

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 4500.  

Additional Information

The Pollination of Proteas:    http://protea.worldonline.co.za/pollinat.htm

 All comments to the author Brian Johnston are welcomed.

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