The Science of Botanical Art

Saprophytes

By Dick Rauh

Originally Appeared in The Botanical Artist, Volume 15, Issue 3

 

There are a number of oddball plants that aren’t green. What this indicates is the lack of chlorophyll, and thus an inability to photosynthesize. Unbelievably, as far as I’m concerned, it is estimated that there are some 3000 species of flowering plants that have no chlorophyll. Until fairly recently, some of these plants were considered ‘saprophytic.’

We thought that they were not parasites, but were able to get their food from organic matter in the soil. As early as the 1950s a Swedish scientist had performed experiments that seriously questioned this belief (even though I was taught it as recently as 2000 when I took my graduate work) and like many “facts” in the world of botany, it takes a long time for acceptance to come, even when girded with irrefutable data. Today we know that no member of the green plant kingdom has the equipment to obtain food from decaying matter. There are bacteria and fungi that are able to perform this necessary function, but these have their own physiology and chemistry, and are in their own kingdoms.

What makes some of these non-green plants so special, and I am talking now about the monotropes (I.e. Indian pipe, squawroot, and pine drops for example), and some non-chlorophyllous orchids ( like coralroots), is the fact that they don’t get their sustenance directly from another plant. Some plant parasites like dodder and mistletoe prey on other plants and the results are obvious, but these, the newly named mycoheterotrophs, are parasites on the mycorrhizal fungi that get their food in turn from trees.

Now that I have you completely confused, let me backtrack a bit and do some basic explanation. First, most plants are autotrophs. Troph comes from the Latin and means nourishment, so that autotroph translates roughly as self-feeder. This is the basis of life as we know it. If it weren’t for the ability of plants to take carbon dioxide and water and the energy from sunlight to make sugars there would be no food for the rest of us. We are known as heterotrophs. We can’t make our own food, so we depend on plants either directly, the vegetarians or indirectly, carnivores, or both, omnivores. I think I may have written about this before, but it’s so important that it doesn’t hurt to repeat myself.

Most heterotrophs are in the animal kingdom, but here are plants that can’t make their own food so like the rest of us they depend on photosynthesizing plants to provide sustenance. All plant parasites lacking green are classed as heterotrophs. The reason why Indian pipe and its relatives (monotropes) are called myco-heterotrophs is because they use fungi (myco is the prefix that means fungi) to act as middlemen to help them obtain sustenance.

A surprising number of species of flowering plants have what is known as a symbiotic relationship with fungi or bacteria. This means that the two organisms live together in a mutually beneficial relationship. Ah, wouldn’t it be nice if humans could take a hint from our botanical friends in this.

Fungi bring to mind mushrooms and their ilk, the visible, and thus paintable manifestations of this kingdom, but these are only the fruiting bodies, the reproductive units, a sporadic part of the fungal life cycle. The fungi vegetative structure consists of vast threadlike networks called mycelium, for the most part hidden underground or inside decaying organisms. It is with these that the roots of flowering plants have congress.

Most of the deciduous trees of the temperate zone rely on special fungi (called micorrhizal) to break down and provide them with essential nutrients, while providing the fungi the food that is the result of the trees’ photosynthesis. This is the wonderful tit-for-tat that we call symbiosis. This applies to any number of wildflowers as well, and is one of the main reasons why certain plants are so difficult to transplant. The rich, beautifully-prepared soil of one’s garden often lacks the fungi that are essential to the health of the plant in the wild.

Now, one of the reasons we thought the monotropes were feeding on decaying matter was the fact that there appeared to be no direct connection from their roots to the roots of another photosynthesizing flowering plant. They were certainly alive, and although they had flowers, most had no leaves and were white or pink, or in some cases red, and thus not making their own food. They had to get their energy somewhere, so organic matter in the soil seemed a natural solution. I think the notion that they were getting their food that way was somehow more appealing than the idea that they might be parasites, with all the negative connotations. I have a feeling that is why the incorrect concept hung on as long as it did.

What is now known about these plants is that they are epiparasites; they prey directly on the micorrhizal fungi, get nutrients from them and then also get the sugars that the fungi have received from their host, while supplying the fungi nothing in return. This doesn’t make the Indian pipe or the coralroot less appealing to paint, it just answers the questions of why there are no leaves, no green coloration, no dependence on the sun so they can grow in deep shade even though they are flowering plants and not mushrooms. The parasitism in this case is so subtle, so slow and out of scale with its food source, that the results are almost invisible to detect and thus seem to ameliorate the negative feelings we get.

  • Sarcodes sanguinea, Snow Plant, mixed media, 13x17”, ©Grace Smith 2002. A California native, snow plant arises from the pine needle mats under redwoods in very early spring.