Nature's Own Floral Shop

Had my students examining plant diversity today, so here's a pretty little collection.

Grass-Pink Orchid (Calopogon pulchellus), Illinois Beach SP,
Lake Co, IL 7/13/2013

Nodding Ladies' Tresses, (Spiranthes cernua), Illinois Beach SP,
Lake Co, IL  9/27/2011

Pink Lady's Slipper, (Cypripedium acaule), Allegheny NF,
Forest (?) Co., PA 6/5/2005

Prairie Fringed Orchid (Platanthera leucophaea),
Illinois Beach SP, Lake Co, IL 7/4/2010

Ram's Head Lady's Slipper (Cypripedium arietinum),
The Ridges Sanctuary, Door Co., WI 5/29/2012

 Rose Pogonia (Pogonia ophioglossoides), Volo Bog SNA,
Lake Co, IL  6/8/2012

These are all orchids. Although we often think of orchids as exotic, tropical plants, they're found worldwide. Most of these are from Illinois, one is from Door County, Wisconsin, and one was shot in the mountains of western Pennsylvania.

There are somewhere around 25,000 named species of orchids, making them one of the largest plant families. Given that they're found worldwide, it's not surprising that a lot of work has been done on them. In recent decades, it appears as if most of that research has focused on systematics, the pace and timing of speciation, and coevolution with pollinators. Ramirez, et al. examined the timing of evolutionary events within the family, and conclude that it dates from the late Cretaceous. (1)

Most plants that rely on insects for pollination supply nectar in exchange. But some orchids have evolved other methods. Calopogon tuberosus, for instance, apparently relies on it's pollinators not recognizing that there won't be nectar. (2) For the most part, though, the trend in orchid-pollinator coevolution has involved specialization, where a species of orchid reduces the number of pollinator species it relies on, often down to one. (3) Despite that, there are quite a few specialized orchids that don't rely on nectar. If you're a bee, though, why visit a flower that you know won't have nectar for you?

Many orchids actually mimic female bees, in some cases even producing pheromones. When the male attempts to mate with the flower, pollen is deposited. In Trigonium obtusum, Singer found an interesting trick that the plant uses to avoid self-fertilization: the pollinaria that carry the pollen are too large to fit in the proper part of the plant for fertilization when they're fresh, but after about 40 minutes they dry out and shrink, thus ensuring a proper fit several flowers down the line. (4)

Orchids produce beautiful flowers, and the rarity and beauty of many has made them favorites of both florists and collectors for centuries. But the next time that you're downtown picking up that corsage, remember just how fascinating these things are before they're picked.

(1) Ramírez, S. R., Gravendeel, B., Singer, R. B., Marshall, C. R., & Pierce, N. E. (2007). Dating the origin of the Orchidaceae from a fossil orchid with its pollinator. Nature, 448(7157), 1042-1045.

(2) Firmage, D. H., & Cole, F. R. (1988). Reproductive success and inflorescence size of Calopogon tuberosus (Orchidaceae). American Journal of Botany, 1371-1377.

(3) Tremblay, R. L. (1992). Trends in the pollination ecology of the Orchidaceae: evolution and systematics. Canadian Journal of Botany, 70(3), 642-650.

(4) Singer, R. B. (2002). The Pollination Mechanism in Trigonidium obtusum Lindl (Orchidaceae: Maxillariinae): Sexual Mimicry and Trap‐flowers. Annals of Botany, 89(2), 157-163.