by Brian Johnston (Canada)
One year after I completed an article on
a flowering begonia, I chanced upon this plant at my local
centre. Although it appeared very similar to the first,
were some strange differences that will be noted in this
In addition, photomicrographs will provide the closer views that
missing in the earlier examination of the Begonia. (Note
some of the descriptive text is identical to that of the
For the botanical layman,
plants are relatively easy to identify. Their fleshy
stems, showy flowers, and distinctive asymmetric leaves set them
from other genera. Unfortunately, an unusual
Begonias is that species throughout the genus can be hybridized
one another, even if they originated on different
This might seem like a good thing, but it has resulted in a huge
of cultivars to be developed worldwide. Distinguishing
these hybrids is a formidable task, and so for the purposes of
article, I will simply consider my plant as a ‘typical
Both its common, and genus names were suggested by Charles
French patron of botanical research. Begonia and Begonia honour Michel
former governor of the French colony of Haiti.
Begonias are monoecious, meaning that
separate male and female flowers on the same plant. Male
are referred to as staminate,
while female ones are called pistillate.
at the centre of the first image in the article is
pistillate, as revealed by its large winged ovary. Just to
left of the central flower are two bud-stage staminate flowers
are missing this ovary structure.
The image below shows the
deep green leaves, and multiple flower-heads. Note the
colouration of the plant’s stems.
Let’s look first at the
buds. It appears as though each flower bud possesses two
but in this genus sepals and petals are indistinguishable, and
are referred to as tepals.
the two tepals are closed like the two sections of a
clam. If you examine the images very carefully, you may be
see that some of the clam-like buds are attached to a green
others are not. I wonder what this means? The answer
course, is that some of the buds are staminate because they are
the ovary structure at the base of the clam. In the left
image all of the buds appear to be staminate. Several
the buds seen in the image on the right are pistillate, as
their light green ovaries. In most bud groups, there are
staminate and pistillate types.
If we look more closely at the
staminate buds, it appears that their surface colouration runs
almost white to a medium pink. All have a random
darker pink dots. These pink dots are also found on the
The plant studied in the
article had many bulbous glandular hairs covering the bases of
their supporting stalks. These glandular hairs are
absent in this hybrid.
Under the microscope, the
‘spots’ can be seen to be composed of tinted, elongated
The images are ‘false colour’ because the ‘Levels’ function in
Photoshop was used to increase contrast.
As the staminate buds open,
two tepals separate to reveal a curved, flattened group of
Closer views of a flower’s
reveal that they are supported by broad, but very short yellow
filaments. Notice the variation in shape and size of the
The presence of the swelled,
ovary at the base of a pistillate flower makes it easy to
The side and top views of such
flower show its basic structure. The unopened bud's
ovary wings have a light pink colouration, while the ovary
itself is a
light green. The ovary’s three wings are positioned 120
When the flower’s two tepals
in the blooming process, its bright yellow pistil is revealed.
Since the pistillate flower’s
is divided into three chambers by its wings, there are three
each with a bi-lobed stigma, and supporting style.
Closer views show each
lobes more clearly, and that the three styles are fused near
connection to the ovary. Notice the bright red line that
this meeting point.
Notice the prominent spots on
body and wings of an ovary.
Under the microscope, the red
colouration appears to be located ‘beneath the surface’. I
suspect that the tinted cells may be located in a layer
beneath the surface one.
As we move closer and closer
elegantly shaped bi-lobed stigmas of a flower, their coatings of
hair-like projections become visible. These fine hairs aid
capture and retention of pollen grains transported by wind or
The following high
photomicrograph shows these hairs clearly.
Begonias are noted for their
asymmetric leaves. Their upper surfaces have approximately
rounded lobes. Note that around a leaf’s perimeter it has
irregular band which is sometimes tinged with red.
leaves contain the chemical calcium oxalate within their cells,
makes them poisonous to animals.)
The underside of a leaf is
colourful than its upper surface. Lighter in colour, with
radial array of prominent veins, the leaf possesses a deep red,
irregular band around its perimeter.
In the earlier Begonia
point of connection of stalk to leaf had a bright red ‘beard’ of
hairs. In this cultivar however, this beard is almost
non-existent. Both stalk, and leaf edge are liberally
with fine colourless hairs, with those on the stalk being
Even the radial veins have
colourless hairs growing from them.
The image on the right below
a photomicrograph of the base of one of these hairs. It
to be pink in colour, but it is not. The hair is
the colour is due to the red spot beneath it.
A mature leaf develops from
hairy structure seen below. At first the tiny leaflet is
pink than green.
Views follow, taken from
showing the interior of the partly furled leaf. The outer
bright red, convoluted, and has many hairs growing from it.
If one of the hairs is
under the microscope, details of its cellular structure can be
(right hand image).
Higher magnifications reveal
elongated cells near its base.
The green material forming the
leaf’s surface is examined next.
The following series of
photomicrographs taken with increasing magnification reveals the
stomata and guard cells that control gas entry into, and egress
the interior of the leaf.
The Begonia studied here grows
a unique root structure that looks like a large tuber called a caudex. The plant’s
from this caudex, which is half beneath the soil, and half
Multiple stems originate from each caudex.
Four views of stems follow
show their pale yellowish-green colouration, and tiny bright red
spots. The length of the stem’s irregular hairs is very
but they tend to be the longest near the attachment point of
A number of strange egg-shaped
objects were visible on structures that I examined under the
microscope. Several examples can be seen below. They
like developing seeds that might be found in the ovary, but this
unlikely, since I did not cut open any of those structures.
The approximately 1500 species
wild Begonias grow in a wide variety of ecological niches, most
tropical and sub-tropical regions. Only one tropical
without native species, and that is Australia!
the world over have developed many cultivars, some to highlight
unusual leaves, and others to showcase particularly colourful
The low magnification, (to
macro-photographs were taken using a 13 megapixel Canon 5D full
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
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of
The photomicrographs were
using a Leitz SM-Pol microscope (using a dark ground condenser),
the Coolpix 4500.
A Flower Garden of
A complete graphical index of
of my flower articles can be found here.
The Colourful World
A complete graphical index of
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
April 2013 edition of Micscape.
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