|Dipsacus fullonum, the common teasel. An "urn" type|
water storage, where dead arthropods collect.
Source: Björn Appel at Wikimedia Commons.
However, the idea that the plant could be deriving some benefit from the dead insects evolved at least as early as 1877 when Francis Darwin, who, possibly influenced by his father's book, Insectivorous Plants published in 1875, submitted a paper on the topic to be published in the Proceedings of the Royal Society of London. Since then, there have been additional field observations and laboratory experimentation, especially those of Miller Christy in the 1920s, but, as F. E. Lloyd noted in his 1942 tome The Carnivorous Plants, there still was no experimental proof of carnivory. So does the common teasel derive any benefit from the prey it captures in the water urn?
The short answer is yes. Now we have experimental evidence that suggests the plants derive benefit from feeding dead dipteran larvae. Peter J. A. Shaw and Kyle Shackleton of Whitelands College, Roehampton University in London described their results in a recent article published in PLoS ONE. They found that while supplemental feedings of larvae to the plant did not increase overall above-ground biomass, both the seed biomass and seed mass-to-biomass ratio were significantly larger in plants that were fed. The authors note that the results need to be replicated, but this initial finding suggests Dipsacus fullonum meets one of the criteria to be considered a carnivorous (or paracarnivorous) plant.
Bravo to the researchers. It will certainly be interesting to see how the carnivorous plant research and enthusiast community reacts to this news. It's still uncertain how the plant derives the benefit from prey, but it's becoming more clear that Dipsacus fullonum is a candidate for status as a carnivorous plant. What exactly is a carnivorous plant, though? The exact criteria for establishing evolved carnivory and not just a happy paracarnivorous accident has been debated for years and will be the subject of a later post.
Shaw PJ, & Shackleton K (2011). Carnivory in the Teasel Dipsacus fullonum - The Effect of Experimental Feeding on Growth and Seed Set. PloS one, 6 (3) PMID: 21445274