Friday Fellow: King Fern

by Piter Kehoma Boll

Ferns make up an amazing group of plants and can have many different shapes and sizes. Some can grow like a tree, the so-called tree ferns, which are the tallest ferns in the world today. However, some other not-quite-tree ferns can also become really large. And one of those is today’s fellow, Angiopteris evecta, known as the king fern, giant fern, oriental vessel fern and many other names.

Native from Indonesia, Australia and many Pacific Islands near the equator, the king fern was discovered by European naturalists in the second half of the 18th century and it soon started to be cultivated as an ornamental plant due to its astonishing looks. The fronds (i.e., leaves) of the king fern are bipinnate, meaning that they have a feather shape, like in most ferns, where the leaflets are themselves formed by smaller leaflets. The shape of those fronds is nothing that special, but their size is amazing, as they can reach up to 9 m in length and 2.5 m in width. About 2 m of its length is formed by the thick and fleshy petiole. This makes them the largest fern leaves in the world, and they are even more incredible because despite this huge size they have no hard, woody tissues to sustain them, relying entirely on the hydraulic pressure of the sap.

The fronds of the king fern are so huge it is very hard to take a good photo of them. Credits of this one to Forest & Kim Starr.**

The rhizome (i.e., stem) of the king fern is also huge. It can reach up to 1 m in diameter and get very long. Most of it lies on the ground, like a fallen tree trunk, but the tip is often vertical and can reach up to 1.5 m in height. Overall, considering the size of the huge fronds, the plant can be up to 7 m high and 16 m wide.

The preferred habitat of the king fern are hot rainforests with very rich and drainable soils and good water availability, often near the coast. The sporangia that grow on the underside of the fronds produce a very large number of spores, which enables the king fern to spread quickly across suitable areas. As a result, it became invasive in some areas where it was introduced as an ornamental plant, such as Hawaii, Jamaica, Cuba and Costa Rica. Other regions where the king fern can potentially become invasive include most of the Caribbean and the tropical forest near the coast in Central and South America, Africa and Southeast Asia.

The thick trunk-like rhizome grows horizontally on the ground, except for its terminal part, which is pointed upward. Photo by Steve Fitzgerald.*

The king fern is traditionally used as a medicinal herb by the Dayak people in Borneo, especially to treat liver problems. The rhizome is highly toxic, but apparently can be eaten after a process to extract the toxins. Studies with extracts of the plant indicated that it has the potential for the development of drugs against HIV-1 and tuberculosis.

And there is one more interesting thing about this species. There are fossil fronds from the Carboniferous, about 300 million years old, that are basically identical to those of the king fern. This suggests that this species is insanely old, and was widespread around the whole world during that time. Later, as the eras passed, it retreated to its current native location in areas near the tropical Indo-Pacific. Now, due to human intervention, it seems that the king fern is about to dominate the whole planet again 300 million years after its last empire.

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References:

Christenhusz, M. J., & Toivonen, T. K. (2008). Giants invading the tropics: the oriental vessel fern, Angiopteris evecta (Marattiaceae). Biological Invasions, 10(8), 1215-1228. https://doi.org/10.1007/s10530-007-9197-7

Kamitakahara, H., Okayama, T., Agusta, A., Tobimatsu, Y., & Takano, T. (2019). Two‐dimensional NMR analysis of Angiopteris evecta rhizome and improved extraction method for angiopteroside. Phytochemical Analysis, 30(1), 95-100. https://doi.org/10.1002/pca.2794

Wikipedia. Angiopteris evecta. Available at < https://en.wikipedia.org/wiki/Angiopteris_evecta >. Access on 30 December 2021.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

** This work is licensed under a Creative Commons Attribution 3.0 Unported License.

Friday Fellow: Black Beauty Stick Insect

by Piter Kehoma Boll

The Cordillera del Cóndor, between Peru and Ecuador, is a very precious region. With astonishing biodiversity, it includes the largest number of plant species per area in South America. And hidden between this diverse flora we can find a peculiar and beautiful creature that is today’s fellow.

Named Peruphasma schultei, it is a stick insect sometimes called the black beauty stick insect. Measuring up to 55 mm in length, with males being smaller than females, this stick insect is medium-to-large-sized compared to other species in this insect order. Although short, they are also very robust, with females being thicker than males, so that they do not actually resemble a stick. The body is mostly black, but the eyes are yellow and the mouth and the posterior part of the small hindwings are red.

A male and a female in captivity. Photo by Wikimedia user Drägüs.*

Like all stick insects, the black beauty stick insect is a herbivore. In the wild, it seems to feed mostly on pepper trees (plants of the genus Schinus), but very little is known about its ecology. When feeling threatened, it erects its small wings and sprays an irritating mixture of glucose and peruphasmal, a substance that is exclusive to this species (and perhaps some closely related ones).

The black beauty stick insect is only known to occur in a very small area of only 5 hectares and is considered a critically endangered species. Nevertheless, it has become a very popular pet worldwide because of its unusual color.

A male feeling threatened and stretching its small wings. Photo by Wikimedia user Drägüs.*

In captivity, the black beauty stick insect can feed on a variety of plants. Captive populations also present some specimens, especially males, in which the wings are pink instead of red, a phenotype caused by a mutation in a gene located in the sex chromosomes.

Although the black beauty stick insect’s natural population on the Cordillera del Cóndor is critically endangered, there is already a significant population in captivity and you can find them for sale on websites that sell pet insects. Is this good news for this species? I am not sure. Can we feel fine knowing that the species is surviving as a pet when its populations in the wild are about to become extinct? What is the point of preserving a species without letting it play its role in the world?

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References:

Conle, O. V. (2005). Studies on neotropical Phasmatodea I: a remarkable new species of Peruphasma Conffile & Hennemann, 2002 from northern Peru (Phasmatodea: Pseudophasmatidae: Pseudophasmatinae). Zootaxa, 1068, 59-68.

McLeod, M. P., Dossey, A. T., & Ahmed, M. K. (2007). Application of attenuated total reflection infrared spectroscopy in the study of Peruphasma schultei defensive secretion. Spectroscopy, 21(3), 169-176.

van de Kamp, T. (2011). The “pink wing” morph of Peruphasma schultei Conffile & Hennemann, 2005 (Phasmatodea: Pseudophasmatidae). Entomologische Zeitschrift, 121(2), 55-58.

Wikipedia. Peruphasma schultei. Available at < https://en.wikipedia.org/wiki/Peruphasma_schultei >. Access on 24 December 2021.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Friday Fellow: Stem Rust

by Piter Kehoma Boll

Parasites are almost as old as life itself and they can be a mild to moderate nuisance to their hosts most of the time. However, by domesticating many species, we humans helped many parasites to thrive and become a greater threat to their hosts and to ourselves.

One of these cases is today’s fellow, Puccinia graminis, a fungus that causes a cereal disease known as stem rust. Known since ancient times, as it is already mentioned in works such as those of Aristotle, this species has become a serious problem in more recent centuries after the expansion of agriculture.

The red rust appearing on wheat plants is a sign of infection.

The stem rust belongs to the order Pucciniales, a group of fungi known as rusts. This name refers to the appearance that they cause in plants after infecting them, as parts of the stem and leaves can look like if they have rusted. Although the stem rust can infect several species, its most important hosts, at least from a human perspective, are wheat and barley, especially wheat.

When the stem rust infects a wheat plant, which occurs in summer, it starts to grow as a mycelium inside the plant’s tissue and, after about 1 to 2 weeks, it begins to produce rust-red pustules that appear mostly at the leaf sheaths, although they can appear anywhere on the plant. These pustules are uredinia and contain many stalked spores called urediniospores.

Cross-section of a wheat leaf showing a stalked urediniospores inside a uredinium. Photo by Jon Houseman.*

The urediniospores are dikaryotic cells, i.e., they have two haploid nuclei inside them, and are easily spread by the wind. When they fall on a new wheat plant, they germinate to produce a new mycelium and infect the new host. This way they can spread asexually across a large area. Infected wheat plants are often smaller, produce fewer or smaller grains, and sometimes can even die if the infection is too severe.

By the end of the wheat’s life cycle, the fungus produces other structures, called telia, which produce a different form of dikaryotic spores known as teliospores. The telia have a black color and the disease is also known as black rust because of this. The teliospores can overwinter without a host. During this period, their two nuclei fuse and, as spring arrives, the teliospore undergoes meiosis and produces four spores known as basidiospores.

The black telia, which produce teliospores, look very different from the uredinia under the microscope. Photo by John Houseman.*

The basidiospores are carried by the wind until they reach the so-called alternate host, a plant in which the fungus reproduces sexually. This host is often a shrub of the genus Berberis (barberry). When the basidiospore falls on a barberry leaf, it germinates to produce a haploid mycelium. This mycelium originates structures known as pycnia, which produce both female hyphae known as receptive hyphae and male spores known as pycniospores. The pycniospores are covered by a sticky honeydew that attracts insects. As these insects move from one plant to another exploring this sweet gift, they carry the pycniospores with them.

Cross section of a barberry leaf showing the pycnia on the upper surface and the large aecia on the lower surface. Photo by Jon Houseman.*

When a pycniospore meets a receptive hypha from another fungus, they fuse and grow into a dikaryotic mycelium that will produce again a different structure, the aecium, that contains again another type of spore, the aeciospore. The aeciospores are carried by the wind from the barberry leaves to the wheat plants, where they germinate and restart the cycle.

Aecia on the lower surface of a barberry leaf. Photo by Marina Gorbunova.**

This is a complex and amazing cycle, isn’t it? However, humans hate the stem rust since ancient times. Its effect on wheat is so important that the Romans even had a whole festival, the Robigalia, dedicated to preventing it. It was a horrid festival that included the sacrifice of a poor innocent dog to Robigus, the “rust god”.

In recent history, the fungus caused serious damage in wheat crops across the world several times, especially in Europe, Asia, and Africa. Many modern cultivars have been selected to be resistant to the stem rust, but the fungus also evolves, frequently originating new strains that are able to bypass the acquired resistance of the plants.

But if the fungus has to infect barberry plants to complete its life cycle, wouldn’t it be enough to avoid having barberry plants near wheat plantations? Kind of, but remember that when the fungus is infecting a wheat plant, it produces urediniospores, which can infect new wheat plants. If you plant different wheat varieties that grow across different times of the year, the fungus can keep infecting new wheat plants asexually, not requiring any barberry.

We, humans, are really very good at making diseases more virulent by trying to prevent them. Aren’t we?

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More rusts:

Friday Fellow: Pear Rust (on 27 April 2018)

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References:

Bhattacharya, S. (2017). Deadly new wheat disease threatens Europe’s crops. Nature News, 542(7640), 145. https://doi.org/10.1038/nature.2017.21424

Lewis, C. M., Persoons, A., Bebber, D. P., Kigathi, R. N., Maintz, J., Findlay, K., … & Saunders, D. G. (2018). Potential for re-emergence of wheat stem rust in the United Kingdom. Communications biology, 1(1), 1-9. https://doi.org/10.1038/s42003-018-0013-y

Wikipedia. Stem rust. Available at < https://en.wikipedia.org/wiki/Stem_rust >. Access on 16 December 2021.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Friday Fellow: Fringed Crownhorn

by Piter Kehoma Boll

The rotifers form a diverse but relatively understudied phylum of animals. They are usually very small, microscopic actually, and frequently mistaken for protozoans, especially ciliates. The only larger ones are the acanthocephalans, a group of parasitic rotifers that were considered a separate phylum until recently.

Most rotifers are free-living and have a row of cilia surrounding their mouth, which, when moving, resemble a wheel spinning, hence the name Rotifera, wheel-bearers. However, many groups are very divergent anatomically, and this includes many sessile species, such as today’s fellow, Stephanoceros fimbriatus, which I decided to call the fringed crownhorn based on the meaning of its scientific name.

A solitary fringed crownhorn in its transparent gel tube. Photo by Ken Koll.*

The fringed crownhorn is found in freshwater environments across Europe and North America. Adult females measure not more than half a millimeter in length and, as said above, are sessile. The body has a shape similar to a wineglass, with a long stalk that attatch it to the substrate, usually submerged vegetation. The head is shaped like an elongate cup, the so-called infundibulum, and five long ciliate tentacles are present at its border. The typical wheel of rotifers is only found in the free-swimming larval stage and disappears during the metamorphosis into the adult form, being replaced by the infundibulum. The body, with the exception of the head, is surrounded by a transparent gel tube that the animal secrets.

A specimen moving in and out of its tube. Credits to Ken Koll.*

The food of the fringed crownhorn consists mainly of smaller organisms, especially algae, bacteria and ciliates. Although the cilia on the tentacles are able to move and generate water currents, they do not seem to be used very often, at least not for prey capture. Most prey items seem to be captured passively, with the organism simply ending up on its own inside the “trap” formed by the infundibulum and its tentacles. Once a prey item is captured this way, the movement of cilia from the fringed crownhorn’s gut sucks the food into the mouth.

Like many rotifers, the fringed crownhorn is a female-dominated species. The majority of the species consists of the so-called amictic females, which only produce diploid eggs (i.e., with two chromosomes of each type) that develop into new amictic females. Under certain conditions, however, the amictic females may produce special eggs that develop into another type of female, the so-called mictic females. Mictic females only lay haploid eggs (with a single chromosome of each type). If the haploid eggs are not fertilized, they develop into males, which are much smaller than females. The males then can produce sperm, which can fertilize the haploid eggs of mictic females, originating new diploid cells that will develop into new amictic females.

A female with several eggs inside its gel tube. Photo by Ken Koll.*

The fringed crownhorn is a tiny but fascinating creature and it is a shame that it is so little studied. This underestimated group of animals certainly hides amazing secrets waiting to be discovered.

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More rotiferans:

Friday Fellow: Pliable Brachionus (on 17 March 2017)

Friday Fellow: Rat Acanthocephalan (on 21 August 2020)

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References:

Hochberg, A., & Hochberg, R. (2015). Serotonin immunoreactivity in the nervous system of the free‐swimming larvae and sessile adult females of Stephanoceros fimbriatus (Rotifera: Gnesiotrocha). Invertebrate Biology, 134(4), 261-270. https://doi.org/10.1111/ivb.12102

Hochberg, A., & Hochberg, R. (2017). Musculature of the sessile rotifer Stephanoceros fimbriatus (Rotifera: Gnesiotrocha: Collothecaceae) with details on larval metamorphosis and development of the infundibulum. Zoologischer Anzeiger, 268, 84-95. https://doi.org/10.1016/j.jcz.2016.09.002

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* This work is licensed under a Creative Commons Attribution 4.0 International License.

Friday Fellow: Pepper Cinnamon

by Piter Kehoma Boll

Most spices in the world come from Europe and Asia, at least the most famous ones. However, a few less known spices can be found natively in other parts of the world as well. Today I will present you one of these little-known spice plants, Canella winterana, known in English as the wild cinnamon or pepper cinnamon.

This tree species is native from southern Florida and most of the Caribbean and usually reaches a height of about 10 m, sometimes growing up to 15 m. The bark is light gray and thick, with many small crevices that break it into small scales.

The flowers starting to open. Photo by Wikimedia user Pancrat.*

The small flowers have five dark-red petals and appear in small inflorescences at the end of the branches. They appear during autumn and are monoecious, i.e., have both male and female organs. All flowers of a single plant tend to open at about the same time and exhibit the female function for about 24h. After that, the female organ dries out and the flowers enter into a neuter phase that can last from as little as 1 h to more than 12 h, but never more than 24 h. After that, the male part finally becomes mature, again in all flowers of the plant at the same time. The small fruits, which are also dark-red when ripe, are eaten by many bird species.

The dark-red fruits. Photo by Wikimedia user Pancrat.*

The bark of the pepper cinnamon has a similar scent to that of the true cinnamon Cinnamomum verum, and it is said to be used in a similar way, hence the name. The fruits can also be dried and used as a spice. Unfortunately, I was only able to find very little information about this culinary use of the plant besides several sources simply stating that it is used like that. Is this use widespread in Caribbean cultures? Is it an important ingredient of some particular dish? If someone can answer those questions, please, leave a comment!

The overal look of the bark. Photo by Alan R. Franck.**

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References:

Makowski, H., Majetic, C., Garrett, P., Johnson, S., Schurr, P., & Moore, R. (2021). Floral scent is different between sexual phases within individuals in a synchronously dichogamous shrub (Canella winterana) but there is no distinct female or male scent profile across individuals. Biochemical Systematics and Ecology, 96, 104270. https://doi.org/10.1016/j.bse.2021.104270

Wikipedia. Canella. Available at < https://en.wikipedia.org/wiki/Canella >. Access on 2 December 2021.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

** This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: European Harvestman

by Piter Kehoma Boll

Harvestmen form a peculiar group of arachnids that are often mistaken for spider, although both groups are not closely related. Across most of Europe and Northern Asia, you can find the harvestman, the species who gave name to the whole group. It’s scientific name is Phalangium opilio, currently known as the European harvestman.

A specimen in France. Photo by iNaturalist user saydelah.*

The body of females reaches about 9 mm in length, and males are slightly smaller, reaching up to 7 mm. However, most of their size lies on their legs. The second pair, which is the longest, can reach up to 54 mm in males and much less in females, about 38 mm. They are often brownish but can have some reddish or black marks as well.

Males have very long legs and long chelicherae. Photo by Pascal Dubois.**

The European harvestman can be found in a wide range of habitats, such as forests and meadows. It is also well-adapted to human-disturbed environments (and which European species is not?), such as gardens, fields, lawns and parks. As a consequence, this species has been introduced in North America, Australia and New Zealand.

Females are chubbier and have shorter legs and chelicerae. Photo by Jason Headley.**

A predator, the European harvestman feeds on a variety of small and relatively soft-bodied organisms, such as mites, aphids and insect larvae. It can also eat insect eggs and dead arthropods. In agricultural systems, it can be an important species to control the population of some pests, such as the corn earworm, Helicoverpa zea and the Colorado potato beetle, Leptinotarsa decemlineata. It has also been observed to feed on the soybean aphid, Aphis glycines, but this species seems to be detrimental to the harvestman’s development, so it would probably not eat it in soybean plantations if other prey are available.

Eating an ant. Photo by Martin Galli.**

During the mating season, which usually occurs around autumn, males fight for the females by pushing eat other, attacking with their chelicerae and grabbing and twisting the rival’s pedipalps. The stronger male usually wins and mates with the nearby female while the other male withdraws. Adults die in winter and the eggs survive to hatch in the next spring. This means two generations of the European harvestman never meet.

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You may also like:

Friday Fellow: Platine Shield Harvestman (on 08 March 2019)

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References:

Allard, C. M., & Yeargan, K. V. (2005). Effect of diet on development and reproduction of the harvestman Phalangium opilio (Opiliones: Phalangiidae). Environmental entomology, 34(1), 6-13. https://doi.org/10.1603/0046-225X-34.1.6

Drummond, F., Suhaya, Y., & Groden, E. (1990). Predation on the Colorado potato beetle (Coleoptera: Chrysomelidae) by Phalangium opilio (Opiliones: Phalangidae). Journal of economic entomology, 83(3), 772-778. https://doi.org/10.1093/jee/83.3.772

Newton, B. L., & Yeargan, K. V. (2001). Predation of Helicoverpa zea (Lepidoptera: Noctuidae) eggs and first instars by Phalangium opilio (Opiliones: Phalangiidae). Journal of the Kansas Entomological Society, 199-204. https://www.jstor.org/stable/25086022

Willemart, R. H., Farine, J. P., Peretti, A. V., & Gnaspini, P. (2006). Behavioral roles of the sexually dimorphic structures in the male harvestman, Phalangium opilio (Opiliones, Phalangiidae). Canadian Journal of Zoology, 84(12), 1763-1774. https://doi.org/10.1139/z06-173

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* This work is licensed under a Creative Commons Attribution 4.0 International License.

** This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: Yellow Soil Centipede

by Piter Kehoma Boll

When we think of centipedes, what comes to our minds are often the ferocious species of the genus Scolopendra, like one previously presented here, but most centipede species are small and lovely creatures living in the soil. They are usually small and with very long and heavily segmented bodies and perhaps you have already encountered one under rocks in your garden.

One of these species is Geophilus flavus, or the yellow soil centipede. It has a Holarctic distribution, i.e., you can find it in North America, Europe, northern Africa and northern Asia. Adults have a light-yellow body with a darker, often orange head with very long antennae. Living in the soil, they lack eyes and, therefore, must rely solely on other senses to orient themselves.

A nice specimen in Russia. Photo by Иван Матершев.*

All adult centipedes have an odd number of leg segments. In the yellow soil centipede, this can vary from 49 to 57 or, more precisely, between 49 and 55 in males and between 53 and 57 in females. Studies have shown that environmental factors such as temperature and humidity can influence the final number of segments, with higher temperatures inducing a larger number of segments and high humidity having the opposite effect.

The eyeless orange head with very long antennae of a specimen in Ireland. Photo by iNaturalist user formicacid.

During the mating period, males often court females and, when they become receptive, deposit their sperm in the form of a spermatophore over a silk sheet, from which the female collects it. The egg clutches often have between 50 and 60 eggs and the female guards them and the young until they are able to look for food alone, which usually takes several weeks to a few months.

The small, narrow and flat body allows the yellow soil centipede to move through narrow crevices in the soil and under the bark of fallen logs. It can also dig its own burrows and create a network of tunnels just like earthworms do and, thus, can help increase soil permeability.

A nice specimen in Lithuania. Photo by Gintautas Steiblys.*

The yellow soil centipede is an active predator and hunts mainly at night, searching for small invertebrates such as earthworms, mites and insect larvae. More active during the summer, it stores energy as fat in its tissues and often spends some months hibernating in the winter.

Like my beloved land planarians, soil centipedes are considered very important predators of the detritus food web, i.e., that which starts with detritivores instead of herbivores. Unfortunately, just like land planarians, soil centipedes are another neglected group of predators and little is known about their role in regulating the invertebrate community in soil ecosystems.

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You may also like:

Friday Fellow: Galapagos Giant Centipede (on 22 February 2019)

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References:

Simaiakis, S. M., Djursvoll, P., & Bergersen, R. (2013, October). Influence of climate on segment number in Geophilus flavus, a centipede species inhabiting Sognefjord in western Norway. In Annales Zoologici Fennici (Vol. 50, No. 5, pp. 247-255). Finnish Zoological and Botanical Publishing Board. https://doi.org/10.5735/085.050.0507

Wikipedia. Geophilus flavus. Available at < https://en.wikipedia.org/wiki/Geophilus_flavus >. Access on 18 November 2021.

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* This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: Common Haircap Moss

by Piter Kehoma Boll

For those who never paid much attention to the mini-world of mosses, these may all look the same. However, as we have already learned with the moss species that have been previously presented here, there is a great diversity among these small non-vascular plants. But what if I told you that not all mosses lack water-conducting tissues, or at least not quite?

To understand this, let’s introduce today’s species, Polytrichum commune, also known as the common haircap moss, among other names. It is found across the whole world in areas with high humidity and rainfall, especially bogs, wet heathlands and along forest streams.

Common haircap moss growing in Canada. Photo by iNaturalist user sarahgrant11111.*

Several things make the common haircap moss a very peculiar moss. While most moss species are only some millimeters tall, sometimes a few centimeters, the common haircap moss can grow to an exceptional height of 70 cm, although it often does not go beyond 10 cm. Young plants are dark green, but the color slightly changes to brown as they age. The leaves are often 6 to 8 mm long but can reach 12 cm. They are narrow and elongate. When dry, they point upward, becoming closer to the stem, but when they get wet they point outward, often curving slightly downward.

The reproduction of the common haircap moss basically follows the same pattern as in other mosses. The dominant phase is the gametophyte, which can produce either male or female gametes. The male gametes travel through the water until they reach the female plants and fuse with the female gametes to produce a zygote, which will grow into the sporophyte that has the typical aspect of a long stem with a spore capsule at the top. Then the sporophyte releases the spores, they germinate to produce new gametophytes.

Sporophytes growing on top of the female gametophytes in Germany. Photo by Christian Kahle.

While most moss species have a single layer of photosynthetic cells on the surface of their leaves, the common haircap moss has them organized into lamellae, ridges that run along the leaves’ length and are one cell thick and several cells tall. The uppermost cells of the lamellae are slightly wider than the others, which makes very narrow gaps to form below them between adjacent lamellae. This microenvironment can retain water in dry conditions, which makes the common haircap moss relatively resistant to desiccation when compared to the average moss.

Cross section of a leaf showing the lamellae of photosynthetic cells. Photo by Hermann Schachner.

But the complexity of this species does not stop there. While a typical moss has no differentiated tissues in its stem and water has to be conducted from cell to cell via osmosis, the stem of the common haircap moss has a central portion formed by enlarged cells adapted to transport water upward, similar to how the xylem of vascular plants work. Around this tissue, another layer of specialized cells seems to be able to work as the phloem, conducting water in the other direction.

Cross section of the stem showing the vascular tissue in the central portion. Photo by Hermann Schachner.

Since mosses are not the ancestors of vascular plants, these structures must have evolved independently in both groups. This suggests that vascularization could evolve again and again to help photosynthetic sessile organisms conquer the land. Perhaps if we humans stop to fuck this planet up, one day a new lineage of vascular plants may evolve from the lovely haircap mosses.

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More mosses:

Friday Fellow: Silvergreen Moss (on 4 November 2016)

Friday Fellow: Spreading Earthmoss (on 12 May 2017)

Friday Fellow: Pellucid Four-Tooth Moss (on 13 April 2018)

Friday Fellow: Red Bogmoss (on 10 July 2020)

Friday Fellow: Impossible Moss (on 6 November 2020)

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References:

Brodribb, T. J., Carriquí, M., Delzon, S., McAdam, S. A. M., & Holbrook, N. M. (2020). Advanced vascular function discovered in a widespread moss. Nature Plants, 6(3), 273-279. https://doi.org/10.1038/s41477-020-0602-x

Wikipedia. Polytrichum commune. Available at < https://en.wikipedia.org/wiki/Polytrichum_commune >. Access on 11 November 2021.

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* This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: African Freshwater Oyster

by Piter Kehoma Boll

Oyster is a term used for a variety of unrelated bivalves. Although most oysters occur in the sea, there are oyster-like bivalves in freshwater environments. One of these freshwater oysters is Etheria elliptica, known as the African Freshwater Oyster.

As its common name implies, the African Freshwater Oyster is found in Africa, including the continent itself and Madagascar. It is, in fact, the only freshwater oyster in Africa and the sole species in the genus Etheria. It is spread across most of the largest river basins in Africa, including those of the Nile, Niger, Volta and Congo rivers, and Madagascar.

Several cemented shells of the African freshwater oyster from Angola. Not a beauty pageant winner. Photo by Rob Palmer.*

The external appearance of the African freshwater oyster is not among the prettiest. Being a somewhat oval-shaped bivalve, this species starts its life with two shells of identical size and shape, which is a typical characteristic of bivalves in the subclass Palaeoheterodonta. However, the African freshwater oyster lies on hard substrates with one of the shells and this one starts to encrust, cement onto the substrate, becoming strongly attached to it and causing the animal do become sessile and asymmetrical. The surface of the shell also becomes very eroded, worn out, in a very short time, which gives it that classical irregular look that we see in the true marine oysters. This is, perhaps, why they are called oysters as well.

Inner (above) and outer (below) surface of a freshly collected shell in Sierra Leone. Photo by iNaturalist user benbarca.**

While the outside is kind of ugly, the inner surface of the African freshwater oyster usually has that beautiful iridescent aspect that most mollusk shells have, which is caused by the presence of nacre or mother of pearl.

Like most bivalves, the African freshwater oyster is mainly a dioecious species, with male and female individuals. However, hermaphrodites are not that rare and seem to have completely functional gonads. Details of their reproduction are not very well known yet, apparently.

An edible species, the African freshwater oyster is an important food source for many human populations across Africa, sometimes being the main protein source and often the main income source for many families. The oysters are often harvested by women during low water levels when the oyster colonies become exposed above the water surface. Tools such as hoes and hammers are used to break them free from the substrate. While this subsistence exploitation is essential for many people, the populations are suffering from overexploitation in many areas. In Madagascar, for example, the populations were so heavily harvested that the species is almost extinct there, and evidence points out that other places are heading toward the same disaster.

The oysters are easy to locate during low water levels, as we can see here in the White Volta River in Ghana. Extracted from Ampofo-Yeboah & Owusu-Frimpong (2014).

Despite being considered a single species at the moment, some preliminary molecular results indicated the existence of at least three different species in the Congo Basin alone. This suggests that more isolated populations, in different river basins, may actually constitute distinct species as well. Thus, some may already have become extinct without our knowledge, such as the heavily depleted populations in Madagascar.

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More Bivalvians:

Friday Fellow: Brown Mussel (on 17 November 2017)

Friday Fellow: Giant Clam (on 14 September 2018)

Friday Fellow: Asian Clam (on 14 February 2020)

Friday Fellow: Giant Thorny Oyster (on 30 October 2020)

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References:

Akélé, G. D., Agadjihouèdé, H., Mensah, G. A., & Lalèyè, P. A. (2015). Population dynamics of freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River (Benin-Western Africa). Knowledge and Management of Aquatic Ecosystems, (416), 06. https://www.kmae-journal.org/articles/kmae/abs/2015/01/kmae140100/kmae140100.html

Ampofo-Yeboah, A., & Owusu-Frimpong, M. (2014). The Fishery of the Freshwater Oyster Etheria Elliptica (Etheriidae) in Northern Ghana: Its Distribution and Economic Importance. Journal of Agriculture and Sustainability, 5(2). https://www.infinitypress.info/index.php/jas/article/view/774

Ampofo-Yeboah, A., Owusu-Frimpong, M., & Yankson, K. (2009). Gonad development in the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in northern Ghana. African Journal of Aquatic Science, 34(2), 195-200. https://doi.org/10.2989/AJAS.2009.34.2.11.898

Elderkin, C. L., Clewing, C., Wembo Ndeo, O., & Albrecht, C. (2016). Molecular phylogeny and DNA barcoding confirm cryptic species in the African freshwater oyster Etheria elliptica Lamarck, 1807 (Bivalvia: Etheriidae). Biological Journal of the Linnean Society, 118(2), 369-381. https://doi.org/10.1111/bij.12734

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* This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

** This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Friday Fellow: Black Wart Lichen

by Piter Kehoma Boll

During their evolution, fungi realized that becoming friends with algae was a successful business, and so this association evolved several times independently, giving rise to a particular type of organism that we call lichen. Three lichens have been presented here previously, the elegant sunburst lichen, the Christmas wreath lichen, and the Pygmy black lichen. And today we have once more a black lichen, Verrucaria nigrescens, or the black wart lichen.

Found across Eurasia and North America, the black wart lichen is a crustose lichen, meaning that it grows on the substrate as a crust, resembling a kind of thick and dry drop of paint, in this case, black paint. Although somehow even in height, the surface of the black wart lichen is rough and crossed by fissures that make it look kind of like a set of tightly arranged warts.

The black wart lichen often looks as if someone dropped some black paint on a rock. Photo by Heikel B..*

Although some lichen species can grow on several substrates, the black wart lichen grows almost exclusively on limestone, eventually appearing on siliceous rocks, but the latter do not seem to be an ideal substrate. But spores cannot move around looking for a better substrate, right? So it is try or die for them.

The color of lichens is often affected by the color of their algal component, but in the black wart lichen the black color is part of the fungal component and the green color of the algae becomes completely masked.

Snails appear to be one of the main grazers of the black wart lichen. Several species have been observed feeding on the lichen’s thallus, sometimes only removing the fungal surface, which exposed the green algal layers beneath it, and sometimes eating the algae as well, exposing the white lower layer of the organism or sometimes even to rock itself by eating the lichen as a whole.

Detail of the black wart lichen’s surface. Photo by Valentin Hamon.*

The preference for limestones makes it very likely to find the black wart lichen growing on human-made structures that are made of limestone or otherwise rich in calcium, such as marble. This may be considered aesthetically unpleasant (which I disagree; a lichen-covered sculpture is very cool) but can also affect the integrity of the structure. Although the black wart lichen is a surface lichen, which means it does not penetrate the substrate with its hyphae, it secrets oxalic acid, which slowly dissolves the rock below it. Studies have also shown that the lichen’s blackness causes a considerable increase in the temperature of the substrate below it, which can make it more susceptible to breakdown. As a result, several techniques have been studied to find effective ways to remove the black wart lichen from surfaces.

On the other hand, a lichen-covered limestone is also protected from the erosion caused by water and, although the lichen increases the rock’s temperature under it when the sun shines on it, lichen-covered rocks have in general a more stable temperature, without strong fluctuations across the day, as the lichen also works as a thermal insulator. It seems, therefore, that we must be careful in judging whether a lichen is indeed harmful to the structure it grows on. Sometimes it will actually protect it.

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References:

Carter, N. E. A., & Viles, H. A. (2003). Experimental investigations into the interactions between moisture, rock surface temperatures and an epilithic lichen cover in the bioprotection of limestone. Building and environment, 38(9-10), 1225-1234. https://doi.org/10.1016/S0360-1323(03)00079-9

Carter, N. E. A., & Viles, H. A. (2004). Lichen hotspots: raised rock temperatures beneath Verrucaria nigrescens on limestone. Geomorphology, 62(1-2), 1-16. https://doi.org/10.1016/j.geomorph.2004.02.001

Fröberg, L., Baur, A., & Baur, B. (1993). Differential herbivore damage to calcicolous lichens by snails. The Lichenologist, 25(1), 83-95.

Osticioli, I., Mascalchi, M., Pinna, D., & Siano, S. (2015). Removal of Verrucaria nigrescens from Carrara marble artefacts using Nd: YAG lasers: comparison among different pulse durations and wavelengths. Applied Physics A, 118(4), 1517-1526. https://doi.org/10.1007/s00339-014-8933-y

Radeka, M., Ranogajec, J., Kiurski, J., Markov, S., & Marinković-Nedučin, R. (2007). Influence of lichen biocorrosion on the quality of ceramic roofing tiles. Journal of the European Ceramic Society, 27(2-3), 1763-1766. https://doi.org/10.1016/j.jeurceramsoc.2006.05.001

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* This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.