One illustration which always me struck as a kid, searching through my father's old collection of scientific books, was a Rube Goldberg-style "mouse-trap" analogy of the very complex nature of a Utricularia trap, which appeared, complete with legend, in 1942's The Carnivorous Plants by Francis E. Lloyd.
The above illustration simply begged the question of how an intermediate -- primitive -- form of such a trap could even operate? Each component is inextricably intertwined and the complexities are not limited to Utricularia, but also include Aldrovanda and Dionaea -- to name but a few.
Pitfall traps seem far simpler to understand during the course of evolutionary development. Heliamphora's rolled leaf, however beautiful and sculptured in appearance, is still "simply" a rolled leaf. Those who have cultivated Cephalotus over the years have no doubt experienced some of the quirky intermediate leaves the plant is in the habit of producing -- strange partial forked appendages or shallow and very non-functional pitchers.
But consider the added complexity of rapid plant movement. It is not enough for Dionaea, for example, to simply close its leaves -- and there is still some disagreement over how that is achieved. Other plants are capable of some partial movement (Mimosa pudica, the so-called "sensitive palnt" comes to mind). In addition, Dionaea also manages to provide a chemical lure, some sensitive time-delayed triggering mechanism (to keep it from closing simply under windy conditions or rain), sieve-like teeth to eliminate overly-tiny prey and, therefore, any unnecessary energy expenditures, a method of hermetically sealing the leaves, and the later resetting of the trap. Then there is the complexity of specifically developing digestive glands and enzymes to deal with its prey. It is not enough that the insect simply rots, as is the case with some primitive pitfall traps.
William Paley posited his famous “watchmaker” teleological argument in Natural Theology in the early nineteenth century, suggesting that the very complexity of nature and the surrounding world begged some form of “intelligent” design and purpose. Others, including David Hume, refuted that populist idea at the time, pointing out nature’s occasional foibles, real defects, and monstrous mistakes. The six-legged calf at a county fair years ago immediately comes to mind -- so too, all other manner of chromosomal anomalies.
Political correctness has unfortunately also struck the scientific world. The concept of "higher" and "lower" animals has now been replaced with the concept of basal (lower) and derived (for the more advanced, but it still means the same damn thing). If we accept the Darwinistic model of gradualistic evolution (and I imagine most of us do) with slow change over millenia, how do we satisfyingly explain the basal rise and directional selection of an organism such as the possible progenitors of Dionaea, Utricularia, or Aldrovanda to the derived plants we have today? Even if we accept Gould and Eldredge and their notion of punctuated equilibria, where evolution is not a linear matter, but can move in "fits" and "bursts" of development, it simply doesn't satisfy that ten-year old kid with the dusty books.
I sometimes wonder whether some of those useless, quasi-functional cultivars of Dionaea that have arisen as the product of tissue culture "excesses" in recent years, offers us a glimpse of just that . . .