A Close-up View of the Wildflower Pineapple Weed

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 blooms.

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). Unlike many other 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 (small flowers) that 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 organs).

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 grains.

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.

Photographic Equipment

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 Coolpix 4500.

References

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, NY.

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.

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.

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