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The orchid and the fungi: true love and mycorrhizal cheating

Posted by: Kirsten Pisto, Communications
Photos by Kirsten Pisto/Woodland Park Zoo

With Valentine’s Day on the way, you might find yourself selecting flowers—perhaps a beautiful orchid—for your partner. But did you know orchids have their own partners?

Orchids and certain fungi share a symbiotic relationship. The idea of symbiosis, whose Greek roots mean “living” and “together,” sounds almost romantic. Yet when it comes to symbiosis—the relationship between two species in which one species is dependent on the other—not all is created equally (i.e. “It’s complicated.”)

Dendrobium speciosum in our Tropical Rain Forest exhibit.

If symbiosis were a box of chocolates (we’re really going hard with this Valentine’s Day theme), it would come in different flavors—some sweet, and some you want to spit out.

Mutualism is any relationship between individuals of different species where both individuals benefit.

Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped.

A parasitic relationship is one in which one member of the association benefits while the other is harmed.

Amensalism is the type of relationship that exists where one species is inhibited or completely obliterated and one is unaffected.

Autumn Flowering Laelia, Laelia autumnalis
Miltassia sp.

For orchids, their complex symbiotic relationship is with certain fungi called mycorrhizae. Luckily for the orchid and the fungi, the symbiosis they share is a sweet one, mostly mutual. Orchid mycorrhiza is the symbiotic process wherein juvenile orchids rely on special fungal symbionts to supply them with carbohydrates and in exchange the fungi receive moisture and access to organic matter.

The roots of an orchid are full of moisture, and often surrounded by organic plant material—the perfect environment for fungi.

The majority of orchids grow in habitats where sunlight is limited (think shadowy mountainsides). Without sunlight it is nearly impossible for the orchids to produce chlorophyll (their version of Vitamin D). Because the orchids cannot produce enough chlorophyll, they depend on specific fungi to assist them. The fungi can digest organic matter that occurs in the surrounding area, converting it into simpler molecules such as sugar that the orchid can absorb.

Pansy orchid, Miltonia phalaenopsis

The young orchid is so reliant on the fungi that it must wait for the fungi to invade its seeds before the orchid even begins to germinate. During this invasion the fungi obtains nutrients from the host plant, while the orchid seeds receive a fungal energy boost (carbon). All orchids depend on mycorrhizae at some stage in their life-cycle.

Orchids rely on the fungus as they begin to grow, but as they mature some species begin to produce their own food source. Some orchids become photosynthetic, meaning they can produce their own organic carbon. While botanists are still researching this complex relationship, it appears that even orchids which are photosynthetic may still use the fungi as a back-up food source.

This all goes down between the root tissue of the plant and the mycelium of the fungus: hard to actually see, but very important!

The dangly root tissue of an orchid stretches out to find moisture, here in the zoo’s greenhouse you can see just how massive the roots appear.

What does the fungi get in return? Moisture and food. The mycorrhizae fungi digests vascular plant material found amongst the roots of an orchid. The fungus also keeps moist due to the water-rich root environment of the orchid.

A humid and moist environment is ideal for both orchids and fungi. Imagine how many awesome fungi live in the zoo’s greenhouse! 
A fungus, such as the white material shown here on this compost heap, covers the roots of the orchid.

Wait, so what is the juicy gossip about mycorrhizal cheaters? It is simply an informal term that refers to a plant which skips the traditional photosynthetic processes and instead gets its food from fungi that grow nearby. The plant is “cheating” the traditionally known method of gathering nutrients.

Burrageara ‘Living Fire’. hybrid between Vuylstekeara Edna and Oncidium maculatum.

What can we learn from this highly exaggerated parallel between love and symbiosis? Give a little, get a little.

Happy Valentine’s Day from our fungi to yours.

Phalaenopsis pallens

Goat-horned Epidendrum, Epidendrum capricornu
Tracy's Cymbidium, Cymbidium tracyanum

Roses are red, 
Violets are blue.
Orchids and fungi,
A love so true!