A Close-up View of a Member of the
Ericaceae Family -

"Pink Heath"

by Brian Johnston   (Canada)

The names heath and heather are often used interchangeably, since they are both ground-hugging evergreen shrubs possessing a profusion of tiny flowers.  Heath however has needle-like leaves, while heather has short, scale-like, overlapping leaves.

A true heath (genus Erica), like the one shown in the article, has urn or bell-shaped flowers.  The genus name Erica derives from the Greek “ereiko” which means to break.  This may refer to the fact that some species of heath stems break easily, or to the medieval theory that the plant could dissolve (break up) gallstones.  Strangely, the term “heathen” was used originally to describe anyone living on the “heath” (a tract of wasteland).  Botanically speaking however, the term refers only to the Ericaceae family.  This family contains about one hundred genera, and over three thousand species of trees, shrubs, and herbs, many of which form the characteristic vegetation of regions with acidic soils like those in moors, swamps and mountain slopes.  The best known members of the heath family are the rhododendrons, azaleas, cranberries, and blueberries.

The huge number of blooms on a single small shrub 10 cm high, and 30 cm in diameter, can be seen in the two images that follow.  The immature flowers are pale greenish-white in colour, and transition through faint pink to deep pink in the mature bloom.  There are so many flowers that the ribbons of dark green needle-like leaves are mostly hidden from view.

An image of a single branch shows these leaves, and a group of immature flowers.  The tightly packed reproductive organs of each flower can be seen protruding from the flower’s tip.

Still higher magnification reveals the details of an immature flower.  At the base, there is an outer ring of five sepals forming the calyx. Each sepal has a brown or orange coloured tip.  An inner urn-shaped white structure forms the corolla, which has five overlapping lobes.  (Put differently, in this flower the petals are fused together almost to the tip forming a tubular, trumpet-shaped structure – the corolla.)  Protruding from the corolla’s lobes are the tightly packed brown anthers, and long thin pistil which can be white or light brown.

If you look carefully at the leaves in the two images that follow, you may be able to see that the upper and lower surfaces of a needle are different.  The lower surface has what appears to be a groove, while the upper surface does not.  Each leaf is about 1.5 mm in width and 12 mm in length.

Higher magnification shows the very noticeable groove in the lower surface more clearly.

Two photomicrographs of the tip of a leaf show the clear difference between the upper (left), and lower (right) surfaces.  The leaf is actually hollow inside, and the interior is covered with many fine, glandular protuberances.  Some of the protuberances can be seen at the edges of the slit-like opening in the leaf’s lower surface.  This slit appears as a groove at lower magnifications, and to the naked eye.

By using a higher powered objective, the protuberances along the edges of the slit (left image) and in the interior of the leaf (right image) are resolved.

The flowers on a stalk mature to their final deep-pink colour in a random fashion.  The images that follow show the many colourations that appear in flowers on a single branch of the plant.  Notice in the darkest coloured (completely mature) flowers, that the dark brown anthers separate and can be seen to be independent of one another.

The bases of branches have fewer flowers than the tips.  In the image below, the woody light brown branch can be seen clearly.  Notice the bulbous, darker brown structure that exists at each leaf axil (point of attachment to the stem).

At the time when the flower reaches its deep pink colour, the sepals take on a distinctive orange colouration.  Notice how the five brown anthers protruding from the corolla lobes are neatly packed to form an upside-down dome from which the single pistil extends.

If one of the corolla lobes (or flower petals) is examined under the microscope, the cellular structure of the central vein (left), and surface (right) is visible.

The image and diagram that follow show the structure of an almost mature heath flower.  Each calyx lobe is about 3 mm long, while the corolla, including lobes, is about 5 mm long.  Heath flowers are extremely small!  Notice how far the thread-like pistil extends beyond the brown anthers.

Under the microscope, the pistil can be seen to be composed of an orange-brown style supporting a slightly larger diameter stigma – the female pollen accepting organ.

Each stamen is composed of an orange-yellow filament supporting a red brown anther (male pollen producing organ), which is split into two sections.  Each section has a deep groove along its length.  There are 5 anthers, (or 10 if you count each section as a separate anther).

Details of an anther can be seen in the two images below.  Notice the white, irregularly shaped pollen grains adhering to a ridge on the anther’s surface (right image).

Phase-contrast illumination shows the irregular shape of pollen grains.

Three additional images of a different anther follow.  Notice the spikes on the ridge shown in the third image.

Notice the difference in the colouration of mature (left) and immature (right) flowers.

At one stage, the outer sepals forming the calyx are a completely different colour than the corolla, and thus stand out visually.

Look carefully at the pink flower just to the left of centre in the image below.  Beneath the flower’s base is the purple-brown stem, and what looks to be a ring of extremely small leaflets.

Under the microscope, the two leaflets overlap at their bases.  I suspect that these are bracts (modified leaves).  Note in the right image, the tiny hair-like projections along the bract’s upper edge.  Several pollen grains have been caught by the hairs.

Although the diminutive flowers of the heath plant are difficult to see with the naked eye, they are marvels of both form and structure when viewed close-up!

Heath doesn’t occur naturally on the American continent, Australasia, and in most of Asia.  It has however become naturalized in areas of Australia and New Zealand.  Here in Canada, it can be purchased as a potted plant for decorative use.

Photographic Equipment

Some 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.

Others 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.  (These produce a magnification of from 0.5X to 10X for a 4x6 inch image.)

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 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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