A Close-up View of Dwarf Mountain Laurel
Close-up View of Dwarf Mountain Laurel
by Brian Johnston (Canada)
Mountain Laurel is sometimes
as “the most beautiful tree” because of its spectacular display
flowers in the spring. Growing to a maximum height of
metres, but normally closer to 2.5 metres, it is a many-stemmed
forming shrub, or small tree. Many names have been
Mountain Laurel, including Sheep Laurel, Lambkill, Spoonwood,
Calico-bush, and just plain Laurel. Several of its names
the fact that all parts of the plant are poisonous.
The hybrid studied in this
Kalmia latifolia ‘Elf
is a dwarf evergreen shrub which grows to about a metre in
height. (My plant was truly dwarf, about 30 centimetres in
height!) Its leaves are oval, and glossy dark green.
buds and flowers start faint pink, but the mature flowers are
pure white. The image at the beginning of the article
typical view of the shrub during the blooming period.
It is the large number, and
shape, of both buds and flowers that set the Mountain Laurel
other plants. Perhaps its most unusual feature is the fact
its bright red anthers fit into pits in the surface of the
corolla, and spring out to release their pollen when disturbed
Even the buds are striking in
plant! A whorl of reddish-green sepals surrounds the immature
and forms the flower’s calyx. The unopened corolla appears
grooved with pink-tipped projections near its base. Within
bud, the flower’s anthers are neatly arranged to fit in the
In the two views that follow,
notice that a bud’s stalk, calyx and corolla are covered with
hairs. Although it is not evident from the photographs,
are glandular, and produce really copious quantities of an
sticky, viscous liquid that rapidly coats ones fingers! It
definitely not be a
to have a taste!
Additional images of unopened
can be seen below.
Much closer views of a bud
individual glandular hairs to be seen.
Even clearer views of these
can be seen in the images of a flower’s stalk and whorl of
sepals. Notice in the last images that thin strands of the
liquid can be seen stretching between hairs, like cobwebs.
The point of connection of
flower’s stalk to the stem is particularly sculptural.
colour contrast between the light green stem, and the red stalks
white hairs. Also notice the pale green pointed leaflets
properly called stipules) that grow from the point of connection
flower stalk to stem.
It is impossible to touch any
of Kalmia latifolia ‘Elf
without getting the sticky fluid on one’s fingers. I have
worked with a plant that was so unpleasant to handle, and that
Under the microscope, the
hairs look vaguely alien. Often the tips of several hairs
glued together by their own fluid.
One result of this phenomenon
that insects that happen to alight on any of the plant’s
instantly trapped by the sticky glue. The small insect
the sequence of images that follows tried valiantly, and
unsuccessfully, for over an hour to escape its adhesion to a bud
The three images that follow
buds in the process of opening. Hints of the flower’s
reproductive structures can be glimpsed through the opening in
In this partly open flower,
round, bright red stigma is visible.
Fully blooming flowers have a
corolla consisting of a single fused petal with a 5-lobed
About half way up the side of the corolla, there are 10 niches
accompanied by corresponding bumps on the outside. When
flower blooms, each pit is filled with a red anther and the
supporting filament is curved down towards the base of the
corolla. Probably as a visual cue to insects, there is a
10-pointed, star-shaped red band near the corolla’s base, with
point on the star pointing towards an anther. Growing from
flower’s centre is a single pistil with a white style supporting
If a section of corolla is
under the microscope, its cellular structure becomes
photomicrograph on the right shows a fold in the corolla.
Much higher magnification, as
the image on the right below, reveals the ridged surface details
Bright red cells from the
star-shaped pattern at the centre of the corolla can be seen
The images that follow show
neat packing of anthers in depressions on the interior surface
corolla, and the bent filaments connected to them.
The slightest touch, caused
by the leg of an insect, causes the anther and its filament to
away from its pit.
If you study the flower in the
image below, you may be able to detect a hint of yellow pollen
When a flower first opens, an
anther’s surface is unbroken, and has a red colour.
As time passes, the red
begins to turn reddish-brown.
Eventually two pores open in
anther, revealing the pollen grains within. (Only one of
pores is visible in the images.) The left image also shows
particularly well, the yellowish stigma pad on top of its style
with their pollen revealing pores open can be seen in the series
below. The pollen grains appear indeterminate in shape.
Below are two images showing
short hair-like protuberances on the surface of a filament.
Here are several images that
show Kalmia latifolia ‘Elf
A still closer view of the
receptive surface of the stigma, with its five ‘bumps’, can be
below. Note also that the two pores on the surface of the
bi-lobed anther, seen below the pistil, are clearly visible.
Notice in the image below,
but three of the anthers have sprung away from their pits.
geometry is such that anthers often strike the style as they
‘spring’. This helps to dislodge pollen from their pores.
surface of a stigma follow.
The two photomicrographs below
the cellular structure of the top edge of the flower’s style
(red), and the stigma dome (yellow).
Even the style has glandular
producing the sticky fluid mentioned earlier.
The plant’s glossy green
start out a much paler shade, and over time, develop the darker
seen at the base of the shrub.
I wonder what the tiny white
might be on the surface of a new leaf? Yes, you’re right;
are glandular hairs! As I mentioned before – every surface is coated with
annoying sticky fluid!
All green parts of Kalmia latifolia contain
poisons andromedotoxin and
arbutin. In case
wish to include them in a salad, it might be a good idea to keep
mind what a medical treatise has to say about the symptoms of
“Poisoning produces anorexia,
repeated swallowing, profuse salivation, depression, lack of
coordination, vomiting, frequent defecation, watering of the
irregular or difficulty breathing, weakness, cardiac distress,
convulsions, coma, and eventually death.”
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.
An 10 megapixel Canon 40D
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
May 2012 edition of Micscape.
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