(alternatively Matricaria discoidea)
by Brian Johnston (Canada)
This common plant often goes unnoticed
by passersby due it its small stature and lack of colourful
petals. Pineapple weed usually isn’t found in the spots that
other wildflowers prefer. It requires compacted, dusty soil like
that found in sidewalk cracks, and footpaths. Although the
literature suggests than individual plants can grow to 25 centimetres
in height, my specimens were a maximum of 10 centimetres high.
As can be seen in the image above,
pineapple weed can appear as a miniature bush with many branching green
stems. The common name is derived from the pineapple scent
produced by the crushed flowers and leaves. A second derivation
originates from the fact that many years ago, the term pineapple
referred to pine-cone shaped structures like those of the plant’s
The two images of a single plant
that can be seen below show a sturdy, flexible stem with many feathery
leaves, and a group of yellow-green flowers at the tips of the topmost
branches. Pineapple weeds grow in locations that result in their
constantly being trod upon. Strangely, such rough treatment
seldom damages this extremely resilient plant.
Up close, the leaves look
distinctly fern-like, and are divided one to three times into short
narrow segments. Leaves are from 1 to 5 centimetres in length.
Pineapple weed is a member of the
Aster family (Asteraceae).
members of this family, the flowers contain only
inner disk flowers. Since no outer ray flowers are present, at a
distance, the flowers may look drab or uninteresting. At higher
magnifications, this conjecture is, as usual, proven to be false.
As the buds begin to open, the
dome-shaped flower-heads appear to be covered by an extremely thin
transparent membrane that eventually splits open to reveal the yellow
pollen covered stamens (male
pollen producing organs) seen in the image at right. Both images
show the multiple rows of green bracts
(modified leaves) with papery white upper margins that enclose the
flower’s base. These bracts are also referred to as phyllaries.
The flower-head below, shown at
higher magnification, reveals these bracts more clearly. The dome of a
mature bloom can be from 5 to 10 millimetres in diameter. Notice
the very large number of disk florets
make up the dome. If you look closely, you
can just discern the four tiny pointed lobes at the top of each floret.
Under the microscope, a complete
floret can be seen to consist of tiny lobes joined to an ellipsoidal
green ovary. (Note that this floret appears to be a mutant,
possessing 5 lobes instead of the normal four!) The brown
structure shown in the image to the right connects the floret to the
base of the flower-head.
Three additional images follow that
show a nearly mature flower-head. The papery upper edges of the
bracts are particularly noticeable.
The mature flower-head contains
florets out of which project brown, bi-lobed stigmas (female pollen accepting
The photomicrograph that follows
shows a side view of a floret with one of the two stigma lobes in
focus. (This floret does have the normal four lobes!) The
stigma becomes dark brown in colour as it ages.
From above, a younger, light brown
stigma can be seen to be covered with spherical semi-transparent pollen
When viewed from a different angle,
the pollen grains appear to be covered with spiked projections.
As a wildflower, pineapple weed is
not a great star. Its flower-heads do however possess a unique
sculptural quality, and a pleasant scent.
Two thirds of the macro-photographs
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.) 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 magnification here is about
14X for a 4x6 inch image.) The remainder of the 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. The photomicrographs were taken
with a Leitz SM-Pol microscope (using a dark ground condenser), and the
The following references have been
found to be valuable in the identification of wildflowers, and they are
also a good source of information about them.
- 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.
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.
- Barker, Joan.
2004. The Encyclopedia of North American Wildflowers.
Parragon Publishing, Bath, UK.
Microscopy UK or their contributors.
Published in the
January 2010 edition of Micscape.
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