On our recent trip down to the Big Thicket in Texas, Laurie and I saw Sarracenia alata (“Pale Pitcher Plants”).
That got me thinking about the Pitcher Plants that I used to see in New Hampshire. Those New Hampshire plants were a different species, Sarracenia purpurosa – the “Purple Pitcher Plant”. I was struck by the big differences in pitcher shape between the Sarracenia alata from Texas and the Sarracenia purpurosa from New Hampshire.
These photos are from a trip that my Dad and I took on a rainy June 28, 2004 to a bog in Henniker, NH.
The bog was small, maybe about an acre. It was a “quaking bog” – we would walk on the waterlogged Sphagnum Moss and the moss would shake and undulate as the water-waves passed through it. The feeling was like walking on Jello. If you stood in one place, you could feel yourself sinking into the thick, water-soaked moss.
It occurred to us that it would be pretty easy to sink up to our necks in soft spots in the bog, or fall into concealed lacunae in the Sphagnum mats. Fortunately, neither of these unfortunate eventualities came to pass.
The bog was surrounded by trees, and the bog’s surface had been invaded by shrubs and saplings. I’d been to this same bog ten or fifteen years previously and I remembered it as being a much more open area. I’m guessing that the site could benefit from a controlled burn.
We saw numerous Pitcher Plants, but we didn’t see any Sundew Plants. Perhaps they were crowded out by the other vegetation?
The Pitcher Plants were in flower. That was pretty neat. Like the Texas Sarracenia alata, these New Hampshire Sarracenia purpuerea blooms were “nodding” on the end of their petioles so that the blooms faced down, towards the ground. The blooms were green, with reddish-purple margins.
These plants were beautiful. The rims of the pitchers were were rolled almost like lips, and were a luscious red-purple color. These lips had a lot of ants on them, possibly a species of Dolichoderus. The ants were mostly stationary – I think they were licking secreted nectar off of the rims of the pitcher.
There were beads of moisture visible on the lips of the pitchers. I suspect most of the moisture was from the rain.
It’s interesting to see the ants on the pitchers. Stephen Heard (1998) found that ants were about 70% of the prey captured by his population of Sarracenia purpurea.
Newell and Nastase (1998) set up video cameras to watch the visitors on Pitcher Plants, then tracked the outcome of each potential prey item. They found that 74% of the prey that were captured were ants.
Additionally, they found an astonishingly low capture success rate – 0.83-0.93%. And, even though ants were the bulk of the captured prey by dry weight, the Pitcher Plant had an even lower capture efficiency on them when compared with other prey species. The Pitcher Plants only a 0.37% efficiency with capturing ants (!).
Bauer etal (2014) came up with a model explaining how temporarily inactive traps in Nepenthes Pitcher Plants could be of benefit to a Pitcher Plant when trapping ants. Their explanation was that temporarily inactive traps allowed Ant scouts to survive and return to the nest, thus recruiting more Ants to come back to the pitchers. Bauer etal’s models showed that this temporary inactivation of traps allowed the Nepenthes Pitchers to capture more ants over the long term.
Perhaps the low capture rate of the the Sarracenia purpurea Pitchers is playing a similar, long-game with its Ants.
It’s interesting to compare the Sarracenia alata pitchers from Texas with these New Hampshire Sarracenia purpurea pitchers.
Here is a photo of some young Sarracenia purpurea pitchers, from New Hampshire:
Sarracenia purpurea pitchers, with surrounding vegetation.
And here is a photo of a young Sarracenia alata pitcher, from Texas:
Pale Pitcher Plant (Sarracenia alata).
Notice how the Texas Sarracenia alata pitcher has a “hood” over the pitcher’s opening, which would keep rain out of the pitcher. Look how the New Hampshire Sarracenia purpurea pitcher opening has no hood. Instead, the S. purpurea opening is flared out in a design that would capture the maximum amount of rain, like a funnel.
The S. alata pitcher opening is small compared to the length of the pitcher, like a champagne flute, while the S. purpurea pitcher opening is relatively wide, like a coffee cup. I think that the difference in shape becomes even more pronounced as the plants age.
Why are the pitchers different shapes? Why does S. alata have a hood over the pitcher opening, while S. purpurea does not? I’ve read that S. purpurea gets almost all of its pitcher fluid from rain water, while other Pitcher Plants typically excrete the water themselves. Presumably, the S. alata is trying to minimize evaporation of its fluid. Perhaps it’s also trying to minimize the dilution of its excreted pitcher fluid by rainwater?
And since S. purpurea is able to rely on rainwater to fill its pitcher, perhaps it can afford to have pitchers that hold a larger volume of fluid than S. alata?
Another thing that might explain the difference in the shapes of the pitcher between the two species – these New Hampshire S. purpurea live in an area that is probably much more likely to freeze than the Texas S. alata. I wonder if the larger volume of fluid in the S. purpurea pitchers gives the pitchers a greater thermal inertia than the ‘champagne flutes’ of S. alata.
Neat stuff, in any case.
Sources:
Bauer U, Federle W, Seidel H, Ulmar Grafe T, Ioannou C. 2014. How to catch more prey with less effective traps: explaining the evolution of temporarily inactive traps in carnivorous pitcher plants. Proceedings Royal Society of Botany 282:20142675.
Heard, Stephen B. 1998. Capture Rates of Invertebrate Prey by the Pitcher Plant, Sarracenia purpurea L. American Midland Naturalist 139:79-89.
Newell, S and Nastase, A. 1998. Efficiency of insect capture by Sarracenia purpurea (Sarraceniaceae), the northern pitcher plant. American Journal of Botany. 85(1):88.
Addendum: I just came across this article by Marc Sudman: A Sarracenia purpurea population in a peatland of Southern New Hampshire (Volume 37 of the Carnivorous Plant Newsletter (March 2008)).
I strongly suspect that his article is about the same bog that my Dad and I visited in this post. How cool is that?
