Mycoheterotrophic Plants A.k.a. Fungus Flowers

By —— Bio and Archives--March 22, 2017

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Walkers in the northern woods can hardly failed to have wondered about them. Pale ghosts in the gloom of the understory, emerging from the leaf litter.

Formerly classed as saprophytes, feeding directly on dead and decaying matter—think famed Triffids of science fiction—they are now known to be botanically even more interesting. And make fanciers of Orchidaceae and Ericaceae take notice.

These non-photosynthesizing plants are not parasitic. They obtain their nutrients by living in a symbiotic relationship with mycorrhizal fungi. The fungi, in turn, are associated with vascular plants. There are believed to be at least 400 species of such plants that totally depend on such relationships and another 20,000 species that are partially so.

Such plants are termed mycoheterotrophic (Greek: mycos = fungus, heteros = another, and trophe = nutrition). Those attempting to get their tongues around the word will be pleased to learn that even specialists abbreviate this to MHPs—Mycoheterotrophic Plant Species.

Less elegantly W. P. Armstrong, who runs the Wayne’s Word website, has called them Fungus Flowers. Walk through the woods and keep your eyes on the leaf litter ad you might find emerging Pinedrops, Pterospora andromedea; Indian Pipe, Monotropa uniflora; Red Snow plant, Sarcodes sanguinea; Coral-root Orchid, Corallorhiza maculata; Candystick, Allotropa virgata, to mention but a few.

There are 15 species of orchid recognized in the Corallorhiza genus. It has long been known that many of North America’s native orchids, in order to germinate and flourish, require the services of specific fungi. Most, however, produce foliage and are capable of photosynthesizing and so, technically are partially mycoheterotrophic. Not so the Corallorhiza, which lack leaves and bear their blooms on upright stems. Spotted Coralroot, C. maculate, is the largest with purple flowers; Northern Coralroot, C. striata, lives up to its name, bearing purple striped petals, while Northern Coralroot, C. trifida, usually has plain white blossoms.

Many other mycoheterotrophic orchids, however, are to be found in the tropics. For example, Gastrodia confuse from bamboo forests of Asia depend on free-living saprotrophic Mycena fungi, representing a genus of 35 orchid species. There is probably more awaiting discovery. Recently, Project Associate Professor Kenji Suetsugu, who specializes in mycoheterotrophic plants, discovered a new species on the subtropical island of Kuroshia (located off the southern coast of Kyushu in Kagoshima prefecture) and named it Gastrodia kuroshimensis.

Even more unusual are the two species of Rhizanthella subterranean orchids from tropical Australia. Its flowers remain underground or perhaps lifting into the base of overlying leaf litter, there to be pollinated, it is believed, by termites and gnats.

What constitutes an MFP is fairly obvious. Those that are partially so may not be so obvious. “Despite considerable progress in our understanding of mycoheterotrophic plants, they continue to present major challenges in scientific investigation . . . There are still many gaps in our understanding of the evolution and ecology of mycoheterotrophic plants,” write researchers in the journal Annals of Botany (vol.104 issue 7). Terminology, too, continues to expand with an explanation published by the journal New Phytologist.

Common plants on the floors of northern forests are the various Pyrola.

Common plants on the floors of northern forests are the various Pyrola. Shinleaf, P. elliptica, is common enough to be recommended by wildflower garden expert Henry W. Art as ‘one of the few eastern North American plants to flower in midsummer in deep shade.’ However, he warns that ‘it is not particularly easy to bring into the garden.’ First Nations members had no such concerns. They used Shinleaf medicinally as a tonic, to alleviate sore throats and canker sores and to treat epileptic seizers in babies. But are these and other Pyrola true examples of partially mycoheterotrophic plants? Suspicions point that way, but botanists appear to still undecided.

Wes Porter -- Bio and Archives | Comments

Wes Porter is a horticultural consultant and writer based in Toronto. Wes has over 40 years of experience in both temperate and tropical horticulture from three continents.

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