A close up view of a Protea: Protea mundii


A Close-up View of a "Protea"

Protea mundii

by Brian Johnston   (Canada)

The origins of the unusual family of flowers called the proteas are unknown.  They are native to Australia and southern Africa, and seem very strange to those of us accustomed to dandelions and thistles.  Botanists sometimes refer to them as distant relatives of the Mistletoe family, although this relationship has been called into question.  Most agree however, that proteas evolved early in the development of flowering plants.  They were perhaps evolution’s early experiments with flower form.

Members of the protea family (Proteaceae) are woody shrubs or trees with hard, leathery leaves that snap rather than fold when bent (sclerophyllous).  Although protea blooms look like flowers, they are actually flower-heads that contain many small individual flowers.  These flowers are enclosed within a cup (called the involucre), formed by overlapping colourful bracts (modified leaves).  The term involucre is French, and is derived from the Latin involucrum meaning a wrapper or envelope.  The bracts (brown and pink in the image above), overlap like the shingles on a roof, and are therefore referred to as imbricate.

Notice in the first image in the article, and the one that follows, the contrast between the intensely hairy pink and brown bracts, and the hairless leaves.  The bracts are covered by what best could be described as “peach fuzz”, which increases in length and density near the tips..

A slightly higher magnification shows that the coverage of the hairs is not complete.  There are seemingly random sections where the density is diminished.

Many of the intermediate and upper pink bracts have brown tips.  Notice the unusual patterns formed by the hairs in the images below.

Only the upper ring of more sharply pointed bracts have long tufts of dense white hairs at their tips.

At the upper limits of normal macro-photography, individual hairs can be resolved.

When examining a bract under the microscope, it is difficult to obtain a clear photomicrograph of the hairs due to the extremely limited depth of field.  In the left image, one plane of hairs is in focus, while in the image on the right, the bract’s surface is in focus.  Note the rounded triangular pollen grains visible in both images.  (Photoshop’s auto-level command was used to increase contrast in the right image.  This produces exaggerated colouration.)

The brown tips of bracts in the lower rings have an interesting furrowed pattern on their surfaces.

This pattern can be seen more clearly in the images below.

The fan-shaped array of hairs at the tips of the topmost bracts can be seen in the three images that follow, taken with increasing magnification.

Notice that the smooth round flower stalk becomes creased with furrows just below the flower-head’s base.

To the naked eye, the lowest brown bracts look rather unsightly.  Up-close however, the pattern produced by furrows and hairs is quite striking.

One of my pet peeves is the fact that many plant leaves have unsightly blemishes caused by insects and disease.  What a pleasure it is to photograph the deep green leaves, and bright red stem of this protea.  They are as close to perfection as nature gets!

A front and side view of a leaf axil (point of attachment to the stem), can be seen below.  Notice the small hairy bump above the axil, that is present for each leaf.  If you look carefully at the image at right you can see that even the stem is hirsute (hairy).

Two images showing the front surface of a leaf follow.  The surface is covered by tiny white specks.  The photomicrograph on the right shows a much higher magnification view of the leaf’s brown edge (seen in the lower left corner of the left image).  The circular structures are the stoma and guard cells that control gas entry into the internal part of the leaf.

The back surface of the leaf shows more prominent veining, and the same specks.  The photomicrograph at right reveals these to be stoma and guard cells.

A view down into the flower-head’s cup reveals a mass of needle-like projections that are reproductive structures.

The two images that follow show the “pollen presenters” of individual flowers located in the base of the flower-head.  These pollen presenters are actually pistils composed of pollen encrusted styles which support tiny bulbous stigmas.  Since proteas are protandrous, the stigma matures later than the anthers, thus reducing the chance of self-fertilization.

Photomicrographs of the red stigma, and lower style can be seen below.  Notice that at this stage, pollen doesn’t adhere very well to the tip of the stigma.

Many of the styles show the strange brown bumps that can be seen in the images below.  (Focus was adjusted between the two images to highlight different details.)

Pollen grains clinging to the lower (left), and upper (right) portions of the style can be seen below.

Higher magnification shows that each grain is roughly triangular in shape.

The shape is easier to see in the still higher magnification dark-ground image on the left, and phase-contrast image on the right.

These larger diameter structures can also be seen alongside the pollen presenters.  Each has a white tufted tip.

A photomicrograph of the tip follows.

Strangely, the structures above are actually tubes, which in time disintegrate and fall away to reveal the pollen presenters seen earlier!  The images below show the stigma, and the top of the supporting style.

For a more complete description of the details of protea fertilization (with images), see my earlier article on the pincushion protea.

Photographic Equipment

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.

The photomicrographs were taken with a Leitz SM-Pol microscope (using dark ground and phase-contrast condensers), and the Coolpix 4500.

Further Information

Protea Atlas Project     http://protea.worldonline.co.za/default.htm

All comments to the author Brian Johnston (bjohnston@idirect.com) are welcomed.

A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.

The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.

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