A Close-up View of a

Gazania Hybrid

Gazania rigens 'Gazoo Red'

by Brian Johnston   (Canada)

This extremely photogenic member of the Asteraceae family is distinctive because of its glossy green leaves and uniquely colourful blooms.  In particular, it has an unusual beige band at the base of its ray floret petals, and the tips of these same petals transition from orangy red to pink.

Like other members of the Aster family, the blooms are actually flower-heads composed of disk florets at the centre, and ray florets around the outer perimeter.  Later in the article, we will take a detailed look at the flower’s reproductive structures.

The Gazania flower was first described in the literature by the German botanist Joseph Gaertner.  It was subsequently named in honour of Theodore Gaza, who is remembered as producing the first Latin translation of the botanical works of Theophrastus.

The flowers of ‘Gazoo Red’, like many other members of this genus, close up at night and on particularly cloudy days.  It is therefore recommended that it be planted in a location that receives full sun.

Side views of a flower-head reveal the whorls of overlapping sepals that together form the calyx.  Notice that the sepals in the outermost whorls bend back, away from the showy ray florets.

From the front, the orangy-pink, outer ray floret petals appear to have many longitudinal ridges.

Viewed from the back, these same petals appear to have a colouration which tends more towards the orange.

Closer views reveal the flower-head’s calyx (left), and the pattern of reddish longitudinal lines on the undersides of ray petals (right).

Higher magnification shows the tiny colourless spikes that grow from a sepal’s edge.

One would expect that all of the flowers on a plant would have identical colour patterns.  This is not the case here.  Notice that although the inner beige band is the same, this flower has much brighter, uniformly red, ray petals.

If one of these petals is examined under the microscope, its cellular structure is revealed.  The shape of an individual cell is remarkably rectangular.

It is amazing that such spectacularly colourful flower-heads can develop from such a humble bud!

Hiding beneath the protective whorls of sepals are the developing ray, and disk buds which have a cream or yellow colour.

In the image below, you can see the dome-shaped, brilliantly white receptacle from which the buds grow. 

Note the particularly sculptural design of the connection of the stalk to the receptacle.  Notice that the pale green stalk is covered with a white membrane which appears to be flaking off in some areas.

It takes about 48 hours for a bud-stage flower-head to go from the stage seen on the left to that seen on the right below.

Still another two days is required for the flower-head to begin to bloom.

Notice that the disk flowers haven't begun to bloom, but the outer ray florets have attained most of their final length.  However, they are still curved in tube-like shapes, and must still uncurl.

The uncurling process has begun in these images, but the ray florets are still positioned to form a cup-shape.

When the flower-head has completely opened, its ray  florets and central disk are almost perpendicular to the stalk.  Note the tight packing of the sepals, and ray floret petals, in the bud shown at right.

It’s time to look more closely at Gazania’s reproductive structures.  In the flower seen below, the ray flowers are in full bloom, but only an outer ring of disk flowers have opened.  The reddish-brown central disk of  the flower-head is composed of unopened disk flower buds.

If we look more closely at the blooming yellow disk flowers, it is evident that each has 5 curled back petals, with a rod-like structure projecting from its centre.  Bud-stage disk flowers have a rounded, reddish-brown tip and yellow base.

These rod-like projections, which are the flowers’ pistils, can be seen more clearly in another, more colourful flower.  One might surmise, from the liberal coating of pollen grains, that these structures were anthers, but one would be incorrect.  In the Asteraceae family, the anthers are hidden deep within the flower’s corolla tube, and as the long stigma, and supporting style extend up through the corolla tube, they brush against the anthers, and pick up a coating of pollen.  In order to discourage self-pollination, the two active surfaces of the bi-lobed stigma are tightly sandwiched together during this process.  Only later do the two lobes of the stigma separate, and become receptive to pollen.  We will see this process later in the article.

Removing some of the sepals and ray florets from a flower-head makes it easier to see the white cone-shaped receptacle from which the florets grow.

The images that follow show the tightly packed disk flowers with their five petals and rod-like, pollen covered pistils.

Closer views reveal that the tips of one of the disk-floret stigmas have separated forming the normal forked, bi-lobed structure.

As mentioned earlier, disk floret buds have rounded reddish-brown tips, and yellow and cream coloured bases.

The first image below shows another stigma that has its lobes separated.  This floret is at the outer edge of the central disk.  The next floret out would be of the ray variety.

These two images, taken of a more brilliantly coloured flower-head, show pistils with unseparated stigma lobes.  If however, you look very carefully at the second image, you can see a stigma where the process of separation has just begun.

If one of the pistils seen in the previous image is examined under the microscope, the red style can be seen exiting through a ring of yellowish-beige anthers.  These anthers do not have the same appearance as those of other plant families.  Here they are elongated with pointed tips, and the pollen generating tissues are on their undersides, facing the style.  Pollen grains can be seen clinging to these anthers, and the base of the style, in the images.

Closer views of the top of an anther reveal its cellular structure.

Here, the transition zone between the top of the style, and the bottom of the stigma, can be seen.  Notice the stubby, hair-like protuberances around the bulge at this location.

Higher up the structure, the two lobes of the stigma have separated in most flowers.  Notice that since the two receptive surfaces were in intimate contact during their trip up past the anthers, there are relatively few pollen grains on the receptive surfaces.

Photomicrographs showing the bi-lobed stigmas can be seen below.  Note the detail on the surfaces of the perfectly spherical pollen grains.

Other views showing sections of these anthers and supporting styles, follow.

No, your eyes are not deceiving you!  The stigma shown in the two images that follow has four lobes – double the usual number!  Obviously this is evidence for the fact that there are no hard and fast rules in botany!

Gazania leaves are a bright, glossy green, and can have a variety of shapes depending on where they are located.  There is one prominent vein on each leaflet.

Higher magnification reveals few interesting details on a leaf’s upper surface.

The undersides of leaflets, on the other hand, are a different story.  A darker green ridge runs around the perimeter of each leaflet, and a wide vein runs its length.  Extremely fine, almost downy hairs cover its surface, and longer, sturdier hairs sparsely cover the stalk.

Some parts of Gazania plants are poisonous, however ingestion usually produces only mild gastrointestinal distress.  It is not recommended to allow pets to eat them.

Photographic Equipment

The low magnification, (to 1:1), macro-photographs were taken using a 13 megapixel Canon 5D full frame 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 macro lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the images.

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

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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