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Photo by Ayinde Listhrop

Plant of the Week: Prairie Dock

By Ayinde Listhrop | September 12, 2017

Towering above all other perennials on the High Line, is one of my personal favorites in the park – the stunningly beautiful prairie dock, or Silphium terebinthinaceum. Growing up to a height of 12 feet tall, Silphium terebinthinaceum puts on a show of long lasting, sun-flower like blooms from early July through September.

Silphium terebinthinaceum is native to the southeastern United States but can now be found as far north as Ontario, Canada, and as far south as Louisiana and Alabama. As its common name suggests it makes its home on the prairies. Moist to dry, black soil prairies, shrub and hill prairies, savannas and limestone glades all make excellent habitats for Silphium terebinthinaceum. It may also occasionally be found growing along railroads and roadsides.

These prairies also host many other plants that can be found on the High Line, including our various Panicum and Schizachyrium species, Sporobalus and Andropogon. As such, Silphium terebinthinaceum is a tough competitor. Its magnificent height keeps its blooms high above the competition for many a wandering pollinator. It features tap roots that can penetrate the soil as deep as 12 feet, allowing the plant store food reserves and collect water in drier conditions. It’s extremely drought tolerant and hardy once established and even recovers quite well from wildfires.

Silphium terebinthinaceum hosts many pollinators in its natural habitat. Long-tongued bees such as bumble bees and honey bees are its primary visitors, but butterflies and humming birds also frequent the flowers. Goldfinches love the seeds and American Bison and cattle graze the leaves and stems.

Silphium terebinthinaceum’s height helps to keep its blooms above the competition on the prairies, as seen here with Andropogon gerardi.Photo by Ayinde Listhrop

The species name Silphium comes from the Greek name Silphion which is an extinct North African plant that produced a resin that was a popular seasoning in ancient Greece and Rome. The specific epithet terebinthinaceum means, “like turpentine” in reference to the aromatic resin in its stems. That said, the resin of the Silphium terebinthinaceum contains chemical compounds that function as a diuretic. It can also be chewed to cleanse the mouth and teeth. Tea brewed from the leaves contain emetic properties and have been used to treat coughs, various lung ailments and asthma. Infusions of the roots are said to be one of the best remedies for an enlarged spleen and have also been used to treat fevers, internal bruises, weakness, ulcers, ailments of the liver and as a general restorative.

There are currently two kinds of Silphium on the High Line. Silphium laciniatum, common name compass plant, and Silphium terebinthinaceum, the prairie dock. There are several key features to distinguish between the two kinds of Silphium. Silphium terebinthinaceum is easily distinguishable by its large coarse, fan shaped basal leaves. Flowers bloom on slender stems in loose airy clusters suspended high above the leaves. Silphium laciniatum‘s leaves on the other hand are deeply lobed and are more evenly distributed along the length of its stems. Flowers bloom much closer to the stem and feature a denser and more robust structure.

Silphium terebinthinaceum (Top left and right) and Silphium laciniatum (Bottom left and right) can be easily distinguished by comparing leaf and flower structure.Photo by Ayinde Listhrop

Silphium terebinthinaceum is a relatively low maintenance perennial. Prefers full sun and average soils. It has the ability to tolerate poor soils but having good drainage is important. Its taproot, which helps the plant tolerate arid conditions, results in the plant being slow to establish and difficult to transplant. Seeds may be collected from September through October and do not require stratification and so they may be sown directly into the soil in spring or fall.

USDA Zone 4-8

You can find Silphium terebinthinaceum in the Chelsea Grasslands between 17th and 20th Sts.

The High Line’s planting design is inspired by the self-seeded landscape that grew up between rail tracks after the trains stopped running in the 1980s. Today, the High Line includes more than 500 species of perennials, grasses, shrubs, and trees – each chosen for their hardiness, adaptability, diversity, and seasonal variation in color and texture. Some of the species that originally grew on the High Line’s rail bed are reflected in the park landscape today. Every week we share one of our gardeners’ current favorites with you.

Our horticultural team counts on members and friends like you to help keep the High Line beautiful and thriving. Join our community of supporters who play an essential role in the High Line’s most important gardening projects.

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TD Bank is the Presenting Green Sponsor of the High Line.