Orchid seeds do not contain sugars, so the seeds take sugars from a mycorrhizal fungus. All orchids are parasitic on fungi while they are seedlings. Because of this unusual relationship, orchids form unique mycorrhizae that differ from both ecto- and arbuscular mycorrhizae.
Ectomycorrhizae are mutualistic relationships formed between trees and fungal species in both the Ascomycota and Basidiomycota. The main difference between ectomycorrhizae (abbreviated EM or ECM) and arbuscular mycorrhizae (discussed last week) is that in ectomycorrhizae the fungus never penetrates the host plant’s cells.
Arbuscular mycorrhizae (AM) are the most abundant type of mycorrhizae on earth. In AM, fungi from the phylum Glomeromycota (FFF#015) penetrate plant root cells and grow arbuscules (tree-shaped structures designed to facilitate nutrient exchange).
Generally speaking, mycorrhizae are mutualistic interactions between the hyphae of a fungus and the roots of a plant. In most cases, the plant gives the fungus sugars in exchange for hard-to-get nutrients like nitrogen and phosphorous. Although there are exceptions to these rules, fungi that are described as “mycorrhizal” usually in the manner described above.
Note: This is an archived post. You can find the current version of this post here. Legend has it that witches use this fungus to cast hexes. When this fungus appears on your gate or door, you have certainly been the victim of a witch’s evil spell. The only way to counter the hex is to pierce the fungus with straight pins, allowing the inner juices to drain and thus killing the fungus and the spell. Unfortunately for those who believe this superstition, this method probably doesn’t work too well for two reasons. First, the mushroom is specifically designed to survive repeated dehydration and rehydration. Second, the main body of the fungus is still living inside the wood. Unless you replace the wood you will probably find the mushroom repeatedly fruiting from the same place.
The Oomycota (literally “egg fungi”) are remarkable organisms because they mimic fungi on a cellular level. They are heterotrophic (get energy from their surroundings) organisms, exhibit filamentous growth, digest their substrate before absorbing it, and produce sexual and asexual spores. For these reasons, the Oomycota were once classified as fungi. They have since been removed from Kingdom Fungi and placed in Kingdom Protista, Chromista, Straminopila, or whatever name it’s going by today. That means it is most closely related to diatoms and brown algae (like kelp). At first this does not seem like a logical grouping because most of these organisms are autotrophic (make their own food). However, there are a few characteristics of the Oomycota that make them more similar to protists than to fungi. For one, the Oomycota have cell walls composed of cellulose, glycan, and similar molecules. Second, they primarily live as diploids (two copies of each...
On this first anniversary of Fungus Fact Friday, I would like to introduce a new topic which I have labeled, “That’s Not a Fungus!” Kingdom Fungi has gone through a lot of changes over the years. Many organisms that were once included in the kingdom have since been exiled. There are two reasons why I think these organisms are worth discussing in FFF. First, they were once studied by mycologists, in some cases contributing more to our understanding of fungi than the fungi themselves. Second, it is important to know what a fungus is as well as what a fungus is not. Slime molds are no longer considered fungi because really the only things those two groups have in common are a similar life cycle and “strange” fruiting bodies. Slime molds do not have cell walls and grow as neither hyphae nor yeast. They also engulf (phagocytose) their food before...
Fungi have developed a variety of ways to trap and kill nematodes. These include: adhesive branches, adhesive knobs, adhesive networks, non-constricting rings, and constricting rings. None of these fungi use nematodes as a primary food source. However, fungi sometimes need extra nutrients, especially nitrogen. Forming traps is very energy-intensive, so they are only formed when nutrients are scarce and nematodes are present. Fungi detect nematodes by “eavesdropping” on ascarosides, the chemicals that nematodes use to communicate with each other. If you want to see these fungi in action and/or get a better understanding of nematophagous fungi, watch the YouTube video (in two parts) linked below*. For your convenience, I have noted the time at which each type of trap is discussed in the video.
These two groups of fungi were recently taken out of the Chytridiomycota and elevated to the rank of phylum. Not surprisingly, both of these phyla produce motile spores (zoospores). The blastocladiomycota inhabit fresh water and soil and fill similar ecological roles to the core chytrids. Many of the blastocladiomycota are pathogens of small, aquatic animals (such as nematodes or water bears), algae, or semi-aquatic plants. The genus Allomyces contains saprobic species often used in experiments. In Allomyces the female gametes secrete the pheromone sirenin to attract the male gametes. The main difference between the blastocladiomycota and the chytridiomycota is that the blastocladiomycota produce an extensive mycelium. Furthermore, only certain cells at the tips of the hyphae produce sexual (male and female, haploid) or asexual (diploid) zoospores. In the core chytrids, the entire thallus is used to produce zoospores.
Phylum microspora (not to be confused with the green algae genus Microspora) contains some of the most unusual fungi: the microsporidia. There are over 1200 described species in this phylum (and that is only a fraction of their biodiversity), divided into about 150 genera (plural of genus). These organisms were originally thought to be protozoans, but recent DNA studies have demonstrated that they belong with the fungi. The microsporidia are all obligate parasites of animals and have an extremely reduced cell structure. They do not have mitochondria, so they can only grow and reproduce within the cells of their host. Their very resistant spores persist in the environment for a long time and allow them to spread from one animal to another. The spores are 1 to 40 micrometers long, making them the smallest eukaryotes. The spores are rougly oval and have a cell wall made of chitin that is...
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