Indicator Species - A Closer Look

Indicator Species - A Closer Look

Silphiums of the Ontario Prairie
photos and text by P. Allen Woodliffe, MNR District Ecologist, Aylmer District
Bluestem Banner - Winter 2007

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Prairie Dock (Silphium terebinthinaceum) and
Compass Plant (S. laciniatum) are two of the largest, most distinctive and best indicators of good quality prairie in Ontario and throughout the tallgrass region. Another member of this genus, Cup Plant (S. perfoliatum), is also a prairie indicator but more apt to be found along wet hollows, prairie streams and woodland edges. All three Silphiums are members of the sunflower family, with large, showy, radiating yellow flowers and large, distinctive leaves.

The name Silphium relates to its resinous character, referring to the gummy material often found along the upper part of the stem when the plant is in flower. Native and pioneer children sometimes used this material as chewing gum. The eloquent natural history author John Madsen, in his 1982 book Where the Sky Began: land of the tallgrass prairie admitted to trying this as gum. However, he concluded that it was “surely the stickiest stuff in all creation and I literally had to clean it from my teeth with lighter fluid.” Given the health risks of doing that, it would not be recommended as a substitute for modern day chewing gum enthusiasts.

Prairie Dock (Silphium terebinthinaceum)
In Ontario this species is restricted primarily to some of the best quality, deep soil prairie remnants of Brant, Essex and Lambton counties, particularly in the Brantford, Ojibway Prairie and Walpole Island areas. It has huge basal leaves that often reach a metre or more in total height, with the stiff, upright, spade-shaped blade itself being 40 cm or more in length. When growing in the open, the leaves of both Prairie Dock and the next species are often oriented in a north-south direction, to enable the maximum exposure to sunlight. Both sides of the Prairie Dock leaf are like coarse sandpaper so in spite of its potential appeal, I can guarantee it was not used as toilet paper even in an emergency, at least not more than once! By early July, a single rigid, shiny stalk arises from the centre of the cluster of basal leaves to a height of 1.5-3 metres or more culminating in a cluster of one to several flower heads. Each flower head is 5-8 cm wide and has 12-25 yellow ray flowers that surround a cluster of sterile disk flowers.

Compass Plant (Silphium laciniatum)
The origin of this species on Ontario’s prairie remnants is not nearly so clear as the previous one. Compass Plant is currently known from railway prairie remnants in Essex, Chatham-Kent and Elgin. Perhaps it was there all along and the railways were established through these prairie remnants. Or perhaps railway cars carrying cattle or hay from the midwest dropped seed of this species as they traveled through these remnants.

There is some justification for both positions, but likely neither will ever beconclusively proven. Regardless, these populations are well established. The population in Chatham-Kent was estimated to be at least one thousand stems, but is somewhat tenuous because the railway line is or may become abandoned. At that point it could easily be disposed of or converted to other uses.

Compass Plant also has very distinctive leaves. With all of their lobes and indentations, they are sometimes described as a giant oak leaf. The entire basal leaf is easily over 60 cm in total length. A stout, hairy stalk arises in mid summer, and may grow to a height of 2.5 metres. A cluster of one to several flower heads are borne at the top, each one being from 6-10 cm in diameter, and having 20-30 yellow ray flowers surrounding a cluster of disk flowers. The roots of Compass Plant are extensive. In the more arid mid-west, they have been documented to a depth of at least 4.25 metres! And the above ground stalk is rigid and persistent. Early pioneers were known to tie bits of cloth to the upper parts of the stalk to mark trails around wet spots or holes.

Cup Plant (Silphium perfoliatum)
This species is locally common in the wetter parts of midwestern tallgrass prairies. In Ontario, it is locally common as well, found primarily along wet prairie or woodland edges. One of the best areas for it is along portions of the Thames River, especially in the Chatham area where tallgrass prairie was historically quite extensive.

Whereas the previously described species had basal leaves that were distinctive, the distinctive leaves of Cup Plant are cauline, meaning growing along the main stem. As shown in the photo, these large, coarsely toothed, upper leaves grow opposed to each other and are joined at the base, forming a cup. These cups often hold water, and birds have been seen drinking out of them.

The square stems of Cup Plant may reach 2.5 metres high, with several flowering branches extending from the upper part of the plant. Each head may be 5-8 cm in diameter, and consist of up to 40 yellow ray flowers surrounding the sterile disc flowers.

The Silphiums could be considered a ready made medicine cabinet. Native people and early settlers alike used them for many things, including treating rheumatism, scrofula and glandular enlargements, as an expectorant, an emetic, for treating coughs and intermittent fevers, as an antispasmodic, to clean teeth and sweeten breath and even for deworming horses!

In Aldo Leopold’s 1949 classic A Sand County Almanac he speculated “What a thousand acres of Silphiums looked like when they tickled the bellies of the buffalo is a question never again to be answered, and perhaps not even asked.” Clearly Silphiums are an integral part of tallgrass prairie. With some of the mega restoration projects going on in the midwest that even include the repatriation of bison to the landscape, perhaps this question can not only be asked, but answered in the future. Fortunately these three species persist at some of Ontario’s best prairie sites as well, although since bison were never conclusively documented in this province, it is unlikely this question will ever be answered on Ontario soil.

Allen Woodliffe