A mistake leads to an unexpected insight

How often do we just muddle along without much clarity of thought? I found myself in this situation when I was returning from a very early breeding bird survey on one of Virginia's highest peaks (Whitetop) and noticed some interesting plants. One of these (see photo) was a mountain wood sorrel, which I mistakenly identified as a Spring beauty, since the flowers are similar (see photo). I realized that the leaves of wood sorrel are similar to those of a shamrock and thus completely unlike a Spring beauty, but discarded this thought. Later, several folks pointed out the error of my ways and I reflected on the similarity of these two flowers which are in completely separate families.

Generally when two plants or animals are quite similar there is a common origin and a close relationship. That is not the case here since wood sorrels (Oxalis) are in a distinctly different family from Spring beauty (Claytonia) which is a relative of purslane and portulaca. So why do the flowers look so similar? The most obvious explanation is that they have converged in structure and color due to similar function. So what do these flowers do? They propagate the species by producing seeds, usually by attracting pollinators. Since the color and form of flowers is closely matched to the type of pollinators, perhaps these two flowers are designed to attract similar insect pollinators? Aside from the color, one of the most distinctive aspects of these two flowers is the pattern of lines radiating from the center. What could be the purpose of such lines? The usual explanation is that they are guides to direct insects to the center of the flower. For example look at the third photo taken in our garden of a native bee (sweat or mason) in the flower of an yellow evening primrose which also has the radiating lines. Some geraniums also show distinct lines in the flowers. So this pattern is not uncommon in unrelated plants.

So why do insects need some help in finding the center of flowers? Flowers sometimes also have a dark throat patch (the so-called nectar guide) to provide an additional cue. Insects primarily use their compound eyes that may have good color vision (plus UV), but their acuity is not as good as ours. Thus they may depend on simple patterns and odor for flower recognition and orientation. It is apparent that flowers find it important to give their pollinators as much help as possible in locating the sources of nectar and pollen. This must facilitate the fertilization of flowers and thus speed the evolution of such adaptations in multiple lines of descent.

So let's resolve to pay a bit more attention out there and enjoy even more the fabulous array of diverse forms of flowers and attempt to fathom what their purposes are.

Bill Dunson
Galax, VA & Englewood, FL