The department has teaching and research interests in many aspects of Biology from the cellular and molecular level to organismal to global ecological and conservation issues

Wednesday, February 16, 2011

Converging for the Birds!

This post was written by Rachel Jabaily, currently a post-doc in the lab of Assoc Professor Tim Motley, about the current display in the Kaplan Orchid Conservatory.

Converging for the Birds:
The plant families Orchidaceae (the orchids-25, 000+ species) and Bromeliaceae (the bromeliads- 3200+ species) are not closely related.  But both have a group of species (genus) in the New World with uncannily similar general flower shape and colors. 

In our living collection we have specimens of the orchid genus Stenorrhynchos, a group of ~7 species found in the SW United States, the Caribbean, Central America, Brazil and much of the Andes.  Notice the red, narrowly opened flowers, each protected by a big bract.

Compare the orchid with these pictures of the bromeliad genus Pitcairnia.  This genus is also only found in the New World tropics but has several hundred species.   See how outwardly similar it appears to the Stenorrhynchos inflorescence (branch of flowers)? The similarity is only skin-deep, though; the bromeliad flower’s reproductive parts (pistil and stamen) do not fuse into a column, which defines the orchid family.

This is a great example of convergent evolution, in which lineages of unrelated organisms evolve in similar ways to similar evolutionary pressures.  In this case, the plants evolved to attract hummingbirds as pollinators, which love red, tubular flowers with lots of nectar at the base.

Interestingly, only ~3% of the world’s orchids are pollinated by birds, with the majority of species using bees, wasps and flies as pollinators. Many orchid species have an extremely specific pollinator relationship with a single insect species.  Bromeliads generally utilize much more promiscuous hummingbirds, and may have fewer species than the orchid family because of it!
We have many other examples of living bromeliads in the Kaplan Conservatory- look UP on the pillars and walls for examples of epiphytes (plants that grow on top of other plants in the rainforest) and DOWN in pots by the entryway for larger specimens that have overlapping leaf bases which hold water like a vase for the plant to use later- also an important water source for many animals!

Here are a few more examples from unrelated plant families that have converged on the hummingbird floral syndrome in the New World tropics

Text and photos by Rachel S. Jabaily, 2011 except photo of Stenorhhynchos: Golden Gate Orchids, and Pitcairnia: J.M. Manzanares