Isle Royale: How did orchids get here?

“Rattlesnake!” I cried out as I stopped abruptly and shifted my pack so I could look down at the ground. Excitement (not fear) was surely evident in my voice, but not many people would recognize the source of that excitement. No snake, but several whorls of grayish-green leaves with white markings hid within the leaf litter along the Minong Ridge Trail on Isle Royale. The checkboard pattern that adorns the leaves is said to look like a rattlesnake’s mottled camouflage, while the broadly oval leaves are similar in shape to plantain leaves (a common plant of yards and disturbed areas). Together, these features resulted in the name “rattlesnake plantain orchid” for this beautiful little plant.

Throughout my hike on Isle Royale, I continued to see clusters of the three different species of rattlesnake plantain orchid along the trail, as well as several other less distinctive orchids, already past flowering. The family Orchidaceae is one of the two most diverse plant families (Asteraceae is the other), and contains more than 22,000 species across the globe. The flowers range from extravagantly beautiful to dinky and unobtrusive. Many orchids have evolved highly specialized pollination systems. Some look just like female bees, and attract amorous male bees to do their cross-pollinating. Many have special landing pads on their petals, and distinctive scents wafting out to entice visitors.

What fascinates me the most, though, is what happens after an orchid is pollinated. The seeds that form are almost microscopic, and over a million of them can fit into the capsule that develops from a single flower. Being so tiny, they lack an endosperm. This little packet of starches, oils, and proteins usually gives seeds the energy they need to germinate, grow their first leaves and roots, and get along until they can sustain themselves. Corn, beans, and squash are great examples of seeds with large energy reserves, and their seeds sustain us, too.

Orchids have found another way.

In order for a dust-like orchid seed to germinate, it must first be infected by a specific fungus. Not all orchids form a symbiosis (a close living relationship between two species, whether or not they both benefit) with the same fungus, but each orchid has just one fungal species, or maybe a few, that will work for it. The fungal mycelia provide the seed with sugar and nutrients in place of the endosperm. It is unclear if the fungus receives anything in return. The seeds can’t germinate without their fungus, except in lab conditions with a source of sugar. Once colonized, a baby orchid plant, called a protocorm, grows, and eventually produces leaves and roots. Some orchids never produce leaves or chlorophyll at all, and live out their days entirely parasitic on a fungus.

Knowing these basics of orchid germination, the question I’d been asking everyone and everything on the island baffled me even more: “How did you get here!?” How could these tiny, fragile seeds make such a long and treacherous journey, 14 to 20 miles across the lake, and then just happen to land where their friendly fungal partner was already established?

My amazement only deepened when I used the latrine near our Rock Harbor campsite for the first time. The educational poster on the inside of the door bragged that Isle Royale is home to 32 species of orchids. Thirty-two times--at least--over just several thousand years, this amazing coincidence happened. Wow.

When I shared my amazement with a mycologist friend, though, he was less impressed. “It’s almost inevitable,” he shrugged. As it turns out, the numerous, minuscule seeds of orchids are well-adapted to wind dispersal – in much the same way that pine pollen drifts on the breeze. That’s how orchids colonize tree trunks in the rainforest. Likewise, fungal spores are often wind-dispersed, even over many miles, and the species of fungi that orchids parasitize are quite common.

A little more research revealed that Ontario –the province just upwind of Isle Royale – has over 50 species of orchids on its mainland. So maybe 32 species on Isle Royale isn’t that impressive after all.

With this new information, my amazement at the simple fact of orchids being on Isle Royale shifted to admiration for the adaptations that brought them to the island in the first place, and the intricacies of their symbiotic relationships. Perhaps my question “How did you get here?” should refer not to the island, but to this moment in time, and the state of exquisite adaptation housed in a ground-hugging, snake-skin patterned cluster of grayish-green leaves.

How quietly, and not with any assignment from us, or even a small hint of understanding, everything that needs to be done is done. – Mary Oliver, Luna

Named for their supposed resemblance to the pattern on a rattlesnake’s skin, rattlesnake plantain orchids are a delight to encounter on the trail. How did they get here? Through millennia of adaptation.Photo by Emily Stone.