A close-up view of the wildfkower 'Garlic Mustard'
View of the Wildflower
by Brian Johnston (Canada)
In Northeastern Canada and the United
States, the biennial, Garlic Mustard is becoming a major menace.
Outcompeting most native plants that bloom in the very early spring, it
forms dense colonies that can be tens of metres in diameter. Near
where I live, the plants’ tall green stems and leaves are the first
sign of spring in forested areas. (This was definitely not the
case even five years ago.) The literal “sea” of Garlic Mustard is
not limited to any particular location however. Anywhere with
moist soil is a perfect place for these fast spreading plants to take
root. Although the same prophesies of doom were given about the
Purple Loosestrife, that menace has not become the scourge that was
predicted. In reality, the Loosestrife plants in my area are very
localized, and their area of infestation has not increased in size over
the past decade.
Alliaria petiolata, native to
Europe and Asia, is a member of the Mustard family (Brassicaceae). It may have
been introduced to North America in the late 1800’s as a food, or
simply by accident. The genus is named after Allium (garlic)
because its species have a similar odour when leaves and stems are
Garlic Mustard’s upper stem leaves are triangular in shape, and deeply
serrated. Newly opened leaves like the ones shown below have a
brownish-green colour, while slightly older leaves are bright green.
The egg-shaped buds of the plant are tightly packed, and beige-tipped.
Occasionally, buds grow from the point of connection of a leaf to its
own stalk The ones shown in the image are very immature.
Blooming flowers have four rounded white petals, and a diameter of
about 0.6 cm.
At a flower’s centre, is a green or brown stalk – the style, that
supports a rounded, pale green stigma (female pollen accepting
organ). Surrounding this pistil are the six stamens.
Each stamen consists of a filament that supports a pale yellow, pollen
encrusted anther (male pollen producing organ). Closer
examination of the image on the right shows that the stamens are
grouped in three pairs – two taller pairs, positioned opposite one
another, and a single, separated pair that is shorter than the others.
While still very immature, the anthers are bright green, with no
apparent pollen on their surfaces (left image). Later, the mature
anther has the “typical” wildflower shape, and it is encrusted with
pollen grains (right image).
Individual pollen grains are approximately egg-shaped, and lack any
large scale surface features.
With the flower’s petals removed, it is easier to see the positions of
the reproductive structures. The image on the right shows clearly
the positioning, and relative size of the three pairs of stamens.
Notice that the pistil is taller than any of the male reproductive
When a flower first opens, the entire pistil has a light green
colour. Notice the rounded top of what appears to be a style
As the flower matures, these style enclosing sheaths turn a
Higher magnification photomicrographs showing the stigma can be seen
below. Its surface is covered with spherically-tipped, glandular
protuberances that help capture, and retain pollen grains.
In the immature stigma shown below, these protuberances have yet to
grow out from the surface. Notice how different are the cells
that compose the surface of the style.
When a large patch of Garlic Mustard appears in early spring, it is
difficult not to admire the green lushness of its new leaves, and
attractive white flowers. However, one must remember what might
have bloomed instead – for example, the beautiful white Trillium, Trillium grandiflorum, (the
provincial flower of Ontario since 1937).
The photographs in the article were taken with an eight megapixel Sony
CyberShot DSC-F 828 equipped with achromatic close-up lenses (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. Still higher magnifications were obtained by using a
macro coupler (which has two male threads) to attach a reversed 50 mm
focal length f 1.4 Olympus SLR lens to the F 828.
The photomicrographs were taken with a Leitz SM-Pol microscope (using
dark-ground and phase-contrast condensers), and the Coolpix
A Flower Garden of
A complete graphical index of all
of my flower articles can be found here.
The Colourful World of
A complete graphical index of all
of my crystal articles can be found here.
- Dickinson, Timothy, et al.
2004. The ROM Field Guide to Wildflowers of Ontario. Royal
Ontario Museum & McClelland and Stewart Ltd, Toronto, Canada.
- Thieret, John W. et al.
National Audubon Society Field Guide to North American Wildflowers -
Eastern Region. 2002. Alfred A. Knopf, Inc. (Chanticleer Press,
Inc. New York)
- Kershaw, Linda. 2002. Ontario
Wildflowers. Lone Pine Publishing, Edmonton, Alberta,Canada.
- Royer, France and Dickinson,
Richard. 1999. Weeds of Canada. University of Alberta
Press and Lone Pine Publishing, Edmonton, Alberta, Canada.
- Crockett, Lawrence, J.
2003. A Field Guide to Weeds (Based on Wildly Successful
Plants, 1977) Sterling Publishing Company, Inc. New York,
- Mathews, Schuyler F.
2003. A Field Guide to Wildflowers (Adapted from Field Book
of American Wildflowers, 1902), Sterling Publishing Company, Inc.
New York, NY.
- Barker, Joan.
2004. The Encyclopedia of North American Wildflowers.
Parragon Publishing, Bath, UK.
Microscopy UK or their contributors.
Published in the
February 2011 edition of Micscape.
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