Wayne’s Word Noteworthy Plant For June 1997
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Wayne’s Word Noteworthy Plant For June 1997
|Many summers ago (about 21 to be exact), a student brought a strange plant to the biology laboratory. The plant resembled a fleshy white fungus, except it had a scaly stem with inconspicuous flowers between the upper scales. It was collected near the Mineral King Game Refuge on the western slopes of the Sierra Nevada in central California, before this pristine area was included within the protective confines of Sequoia National Park. [Thus protecting this lovely forest and meadow wonderland from greedy developers who wanted to convert it into a fancy resort area.] After several hours of careful examination, we concluded that our mystery plant was indeed a “fungus flower,” specifically known as fringed pinesap (Pleuricospora fimbriolata). Because their method of obtaining nutrition is very similar to that of wild mushrooms, fungus flowers are called “mycotrophic wildflowers” by botanists. [Mycotrophic literally means "fungus nutrition."] Our remarkable discovery that fateful summer afternoon eventually led to an extensive (obsessive/compulsive) search for more of these amazing flowering plant species throughout the forested mountains of the Pacific United States.
In natural forest ecosystems throughout tropical and temperate regions of the world, many plant species depend on symbiotic soil fungi living in their root systems. This is especially true of coniferous forest ecosystems. The microscopic fungal filaments (called hyphae) greatly increase the surface area of the root systems and facilitate the absorption of water and mineral nutrients from the soil. In return for this vital service, the photosynthetic trees reward their fungal partners with energy-rich carbohydrates and amino acids. The remarkable relationship has been termed mycorrhizae, and literally means “fungus-roots.” This fungus-root relationship is so widespread throughout forested regions of the world, that some of the familiar mushroom-like reproductive bodies pushing out of the forest soil are actually coming from these extensive mycorrhizal fungi. But of all the mycorrhizal associations, perhaps the most amazing are the strange and unusual flowering plants that are also intimately connected to this fungus-root partnership. Since many of these “fungus flowers” lack chlorophyll and are incapable of making their own energy-rich carbohydrates, they are absolutely dependent on the photosynthetic forest trees. Known as “mycotrophic wildflowers” in botanical circles, some of these fleshy white flowers superficially resemble a moist fungus as they push out of the soil. They certainly include some of the world’s truly bizarre flowering plants.
Flowering plants have colonized and exploited practically every conceivable habitat on earth, and the mycotrophic wildflowers are one of the best examples of this “adaptive ingenuity.” Using labeled sugars containing radioactive carbon 14, scientists have shown that carbohydrates synthesized by nearby forest trees pass into the mycorrhizal soil fungi and eventually into the mycotrophic “fungus flowers.” Since they are living parasitically on fungi that are in turn parasitic on the roots of trees, these amazing flowers have been termed epiparasites (a parasite on a parasite). Unlike true root parasites, such as the broom-rapes (Orobanche species), they are not directly parasitic on the host trees. They have essentially developed a niche similar to that of a mushroom. But unlike fungi, they are true vascular plants with flowers and seed-bearing capsules.
Soil fungi develop from spores that grow into slender, tubular threads called hyphae which may be septate or nonseptate (i.e. without cross-walls) depending on the species. A mass of intertwined hyphae is collectively referred to as a mycelium. Under optimal conditions the hyphae often grow very rapidly, and it has been estimated that if all the hyphae produced in a day by a single soil fungus were laid end to end, they could extend for nearly a mile. Some mycorrhizal associations can be enormous, particularly in coniferous forest ecosystems. A single individual of Armillaria bulbosa has been discovered that permeates more than 30 acres of forest soil in northern Michigan and may be the world’s largest living organism. Some scientists speculate that it was spawned by a single spore thousands of years ago. Another Armillaria in Washington was recently found to consist of a subterranean mycelial network with erect, above-ground mushrooms covering more than a thousand acres of forest soil. These fungal monstrosities are rivaled in total size and mass by a 106 acre, 6,000 ton stand of genetically identical quaking aspen (Populus tremuloides) in the Rocky Mountains. The aspen clone is connected by a common root system, and has literally climbed over mountains and across meadows. Any discussion of massive clonal colonies should also include the conjoined polyps of coral reefs. However, the question still remains: Do these clonal colonies qualify as a single individual, as in the 1200 ton General Sherman giant sequoia (Sequoiadendron giganteum) of California’s Sequoia National Park?
Although the appearance and mode of nutrition of mycotrophic wildflowers is certainly fungus-like, there are other fungal characteristics among vascular plants. Pollen tubes not only resemble the growth of fungal hyphae, but in pines, cycads and Ginkgo biloba they are branched and actually absorb nutrients from the female “host’s” tissue (megasporangium). The multinucleate, cellular tubes (laticifers) found in many members of the euphorbia family (Euphorbiaceae) and milkweed family (Asclepiadaceae) are very similar to fungal hyphae. These fungus-like vessels produce the characteristic milky, latex sap of these two plant families. Some parasitic flowering plants, such as certain dwarf mistletoes and the minute Pilostyles thurberi of the Colorado desert, live completely within the host and only emerge from their host to produce flowers. The vascular tissue of these endoparasites literally permeate the host tissues and truly resemble fungal hyphae.
Although most general botany textbooks suggest that land plants evolved from ancestral green algae, some authorities believe that land plants are comparatively too complex, diversified too quickly, and contain numerous fungus-like cells. In fact, Dr. Peter Atsatt of the University of California, Irvine (Ecology Vol. 69, 1988) suggests an algal ancestor containing a symbiotic, mineral absorbing fungus similar to mycorrhizal associations. Atsatt’s hypothetical ancestor would be similar to a lichen with a dominant algal component. Although Atsatt describes a possible nuclear fusion between the algal and fungal cells resulting in a hybrid genome containing the traits of both parents, his provocative hypothesis has not been widely accepted by evolutionists.
In the shady coniferous forests of the Pacific coastal states there are several spectacular examples of “fungus flowers.” Since many of these mycotrophic wildflowers are nonphotosynthetic, they were once thought to be saprophytic (i.e. surviving on nutrients from decaying organic matter in the soil). Today we know that these species are getting their organic nutrients from nearby forest trees via a microscopic conduit system of mycorrhizal soil fungi. It is a virtually untapped food source that these unusual flowering plants have exploited. Most of these species are now placed in the Indian pipe family (Monotropaceae) or the closely-related heath family (Ericaceae), although they were once placed in the wintergreen family (Pyrolaceae). The fabulous orchid family (Orchidaceae), the world’s second largest plant family, has also tapped in on this food source with several mycotrophic species. Some fungus flowers are cream-colored and fleshy like a fungus, including Indian pipe (Monotropa uniflora), gnome plant (Hemitomes congestum), California pinefoot (Pityopus californicus), and fringed pinesap (Pleuricospora fimbriolata). The name “pinesap” may refer to the fact that these plants commonly grow under pines (or other conifers) and “sap” their juices. Another ghostly white plant of the shady Pacific northwest forests is the rare phantom orchid (Cephalanthera austinae). Some of these pale fungus flowers are not commonly seen by casual observers, and could easily be mistaken for the fruiting body of a fungus.
Other mycotrophic wildflowers are quite colorful, including the pinkish-red pinedrops (Pterospora andromedea) and American pinesap (Hypopitys monotropa), the brilliant red snow plant (Sarcodes sanguinea), the striking red and white-striped candystick (Allotropa virgata), and the lovely coral-root orchids (Corallorhiza maculata and C. striata). Candystick is absolutely unforgettable, a spectacular wildflower that resembles a red and white-striped peppermint stick placed in a Christmas stocking. All of these curious wildflowers develop from a mass of fungal hyphae and tree roots deep in the ground, and in Corallorhiza this fleshy mass resembles a clump of soft corals. The taxonomy of mycotrophic wildflowers is discussed in detail by Dr. Gary D. Wallace in the Wasmann Journal Of Biology Volume 33, 1975.
But of all the fungus flowers, the snow plant is one of the truly spectacular wildflowers of the Sierra Nevada and Peninsular Ranges of California. It was reportedly one of the favorites of legendary naturalist John Muir. Resembling a thick, fleshy, brilliant red asparagus pushing out of the pine needles (duff layer), it is an unmistakable blossom. Although snow plants occur in the San Jacinto and Santa Rosa Mountains to the north and the Sierra San Pedro Martir to the south, they apparently skip San Diego County (the home of WAYNE’S WORD). For this reason they are conveniently called “negative disjuncts.” Snow plant sitings have been reported from the Cuyamaca Mountains, but no voucher specimens are on file at the San Diego Museum of Natural History; hence, the official residency status of this remarkable wildflower in San Diego County remains an enigma.
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