A Close-up View of a Flowering Begonia

Begonia x hybrida

Family Begoniaceae

by Brian Johnston   (Canada)

For the botanical layman, Begonia plants are relatively easy to identify.  Their fleshy jointed stems, showy flowers, and distinctive asymmetric leaves set them apart from other genera.  Unfortunately, an unusual characteristic of Begonias is that species throughout the genus can be hybridized with one another, even if they originated on different continents.  This might seem like a good thing, but it has resulted in a huge number of cultivars to be developed worldwide.  Distinguishing between these hybrids is a formidable task, and so for the purposes of this article, I will simply consider my plant as a ‘typical Begonia’.  Both its common, and genus names were suggested by Charles Plumier, a French patron of botanical research.  Begonia and Begonia honour Michel Begon, a former governor of the French colony of Haiti.

In fact, the subject of this article was in rather ragged condition when I spotted it in the ‘marked-down’ area of the greenhouse.  Since it was the only Begonia in bloom at the time, I decided to take a chance and bring it home, in the hope that it would survive until I finished photographing it.

The first image in the article shows the plant’s deep green leaves, and multiple flower-heads.  Below are two images showing Begonia flowers - flowers that are distinctly different in shape than those of most other plants.

Begonias are monoecious, meaning that they have separate male and female flowers on the same plant.  Male flowers are referred to as staminate, while female ones are called pistillate.  All of the flowers shown in the two images below are pistillate, as revealed by their three bi-lobed stigmas.  It appears as though each flower possesses two petals, but in this genus sepals and petals are indistinguishable, and so both are referred to as tepals.

One of the stems supporting a group of flowers can be seen in the two images that follow.  The many pale green tri-lobed structures are the ovaries of pistillate flowers.  Note at the very top of the stem, several oval leaflets which have no connecting stalk.  Such leaflets are referred to as ‘clasping’.

These clasping leaflets occur only in the top-most section of each of the plants stems.

Closer views of a leaflet reveal its serrated edge, and several reddish, irregular longitudinal stripes.

The Begonia studied here appears to grow from a unique root structure that looks like a large tuber called a caudex.  The plant’s stems grow from this caudex, which is half beneath the soil, and half above.  The visible portions of several of these root structures can be seen below.  Multiple stems originate from each caudex.  Notice the strange ribbon-like hairs that grow profusely from the bases of stems.

Several additional ground level views of the plant can be seen below.  Notice in the first image that the green surface of the caudex is covered with irregular brown scales that are loosely attached.  During hard times, the plant can lose all of its foliage until nothing remains but the caudex.  When conditions improve, the plant is able to regrow stems, leaves, and flowers.

Three views of stems follow that show their pale yellowish-green colouration, and tiny bright red spots.  The length of the stem’s irregular, ribbon-like hairs decreases as one moves up the stem.  Similar rough-looking hairs appear to grow from both upper and lower leaf surfaces.

Closer views of the surface of a lower stem reveal the structure of these strange hairs.  Many are quite long, and have apparently dried out to become thread-like near their tips.  It’s interesting to note that all of the hairs originate from the bright red, irregularly shaped spots on the stem’s surface.

Upper stems appear to be divided into bamboo-like sections by raised rings.  Notice how the stem’s colouration,  number and intensity of spots, and hair length changes above the ring shown in the second image.

Here are a couple of images showing bud-stage Begonia flowers.  In each bud the two tepals are closed like the two sections of a clam.  If you examine the images very carefully, you may be able see that some buds are attached to a green base, while others are not.  I wonder what this means?

The answer of course, is that some of the buds are pistillate, and some are staminate.  The two seen at the bottom of the image on the left below are pistillate, as evidenced by their light green ovaries.  The bud at the top of the image (which is seen close-up in the right hand photograph), is staminate.

Still closer views of this male bud can be seen below.  Notice that both its tepals, and its stalk are covered with bulbous-tipped glandular hairs.  Most hairs emanate from the red spots on a surface.

As you can see below, the stalks of both male and female buds may grow from the same junction on the stem.

Additional views of glandular hairs follow.  Note in the left image, the two tiny leaflets that join the stalk just beneath a bud.

Two images can be seen below that reveal pistillate buds in the process of blooming.

When fully open, the two tepals that form the flower’s combined calyx-corolla are positioned almost in a plane.

Let’s now take a closer look at the male staminate flowers of the Begonia.  In terms of the flower’s tepals, they are identical to pistillate ones.  However in this case there is a cluster of stamens at the flower’s centre.  In this particular species, the stamens are grouped in an asymmetric, (or zygomorphic) mass that resembles a bunch of bananas.

Higher magnification shows that each bright yellow anther is supported by a short, pale yellow-green filament.

A view from above the group of stamens shows how tightly they are packed side by side in the cluster.

Front and side views of a cluster reveal that all stamens have a similar curvature.

Now let’s look more closely at pistillate flowers.  Here there are three bright yellow stigmas, each with two lobes at its tip.

Much higher magnification reveals that the surface of each bi-lobed stigma is entirely covered by fine hairs that increase its surface area, and thus help to acquire, and retain pollen grains.  Notice also that the styles supporting stigmas are stocky and curved.

A side view of a female flower shows clearly that the three pistils are connected to an impressively large, light green ovary which possesses three thin, but broad, lighter coloured ‘wings’.  (The third wing is not visible in the photograph.)

Begonias are noted for their asymmetric leaves.  The upper surface of one such leaf which has 8, pointed, serrated lobes is shown below.  The image on the right shows the strange bright red ‘beard’ composed of coarse hairs that grows from the point of connection of the stalk to the leaf.

A view from beneath the same leaf shows that its underside has a bright red colouration!  The image on the right shows a different view of the ‘beard’ mentioned above.

More highly magnified views of the underside of a leaf can be seen below.  Notice the many hairs that grow from the leaf’s surface, and edge.  Begonia leaves contain the chemical calcium oxalate within their cells, which makes them poisonous to animals.

The approximately 1500 species of wild Begonias grow in a wide variety of ecological niches, most in tropical and sub-tropical regions.  Only one tropical region is without native species, and that is Australia!

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.

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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