Tag Archives: Pteridophyta

Friday Fellow: Giant Salvinia

by Piter Kehoma Boll

We are moving out of the sea this week, but will still remain in the water to bring you a peculiar fern. Commonly known as giant salvinia, kariba weed or giant watermoss, its scientific name is Salvinia molesta and it comes from southeastern Brazil.


Fronds of Salvinia molesta growing in Hawaii. Photo by Forrest & Kim Starr.*

The water salvinia is an aquatic fern that floats on the surface of the water and has a peculiar anatomy. It lacks roots, and it produces leaves in sets of three. Two of them remain at the surface of the water, side by side, and the third one is submerged, acting like a modified root. The upper side of the surface leaves (which are anatomically their underside) have many small hairs that turn them into a waterproof surface and the underside have very long hairs that look like roots.

Preferring slow-moving waters, the giant salvinia grows very quickly in ideal conditions and has become an invasive species in several parts of the world. It was exported from Brazil to be used in aquaria and garden ponds and ended up in natural environments. While spreading, the giant salvinia can cover the entire surface of water bodies, blocking light for other plants and algae, which decreases photosynthesis and reduces the amount of oxygen in the water. Additionally, it can clog waterways, blocking natural or artificial water flows.

The problem caused by the giant salvinia in areas where it has become invasive led to the development of control methods. One of the simplest methods is simply removing the plants mechanically, but it is difficult in areas with large infestations, as even small remaining populations may quickly recover. Another alternative is the use of biological control using Cyrtobagous salviniae, a tiny weevil that feeds on the giant salvinia in its natural environment.

Not everything about the giant salvinia is bad, actually. Its peculiar leaf anatomy led to the discovery of what was properly called “the salvinia effect”, a phenomen by which an air layer becomes stable over a submerged surface, as in the leaves of species of Salvinia. By developing artificial structures that make use of this phenomenon, it is possible to produce devices that move smoothly in water, such as ships with reduced friction.

A considerably recent study also found out that some compounds extracted from the giant salvinia are effective in the control of human tumor cells.

Our relationship with this peculiar plant is therefore one of love and hate.

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Coetzee, J. A.; Hill, M. P.; Byrne, M. J.; Bownes, A. (2011) A Review of the Biological Control Programmes on Eichhornia crassipes (C.Mart.) Solms (Pontederiaceae), Salvinia molesta D.S.Mitch. (Salviniaceae), Pistia stratiotes L. (Araceae), Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae) and Azolla filiculoides Lam. (Azollaceae) in South Africa. African Entomology 19: 451-468.

Li, S.; Wang, P.; Deng, G.;  Yuan, W.; Su, Z. (2013)  Cytotoxic compounds from invasive giant salvinia (Salvinia molesta) against human tumor cells. Bioorganic & Medicinal Chemistry Letters 23(24): 6682-6687.

Wikipedia. Salvinia molesta. Available at < https://en.wikipedia.org/wiki/Salvinia_molesta >. Access on February 21, 2018.

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Friday Fellow: Mexican Giant Horsetail

by Piter Kehoma Boll

If you are walking through the forest of Central America, you may end up finding something that at first you could think is a group of bamboos, plants growing as a cylindrical segmented stem that can reach up to 7 m in height, as seen in the picture below:


A group of bamboos? Not exactly. Photo by Alex LomasAlex Lomas.*

Those are not actually bamboos, though, but specimens of the largest species of horsetail that exists today, the Mexican giant horsetail, Equisetum myriochaetum. It can be found growing naturally from Peru to Mexico in areas of fertile soil, especially along water bodies such as streams and swamps.

As other horsetails, the Mexican giant horsetail has an erect and hollow stem with very narrow leaves growing in a whirl around the “joints” of the stem. The leaves are very simple, similar to those of more primitive plants such as the spikemosses and ground pines, but are thought to be a simplification of more complex leaves, as they are more closely related to the complex-leaved ferns.

More than only the largest horsetail in the world, the Mexican giant horsetail is an important medicinal plant in Mexican folk medicine, being used to treat kidney diseases and type 2 diabetes mellitus. And as in many other occasions, laboratory studies confirmed that water extracts from the aerial parts of E. myriochaetum do indeed reduce the blood glucose levels of type 2 diabetic patients without reducing their insulin levels. One more point to traditional medicine.

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EOL – Encyclopedia of Life. Equisetum myriochaetum. Available at <http://eol.org/pages/6069616/overview&gt;. Access on March 4, 2017.

Revilla, M., Andrade-Cetto, A., Islas, S., & Wiedenfeld, H. (2002). Hypoglycemic effect of Equisetum myriochaetum aerial parts on type 2 diabetic patients Journal of Ethnopharmacology, 81 (1), 117-120 DOI: 10.1016/S0378-8741(02)00053-3

Royal Botanic Garden Edinburgh. Equisetum myriochaetum. Available at <http://www.rbge.org.uk/the-gardens/plant-of-the-month/plant-profiles/equisetum-myriochaetum&gt;. Access on March 4, 2017.

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Friday Fellow: Samambaiaçu

ResearchBlogging.orgby Piter Kehoma Boll

It’s more than time to bring a fern as a Friday Fellow, and I decided to start with one of my favorites, the Neotropical tree fern Dicksonia sellowiana, known in Brazil as Samambaiaçu or Xaxim.


A samambaiaçu in a forest in southern Brazil. Photo by Wikimedia user DeadWood II.*

The samambaiaçu occurs from southern Mexico to Uruguay and is usually found in moist forests, being a remarkable species of moist forests in southern Brazil, especially in Araucaria moist forests. It may reach several meters in height and the fronds (leaves) reach up to 2,4 m in length.

During most of the 20th century, the fibrous stems of the samambaiaçu (usually called “xaxim”) were extensively used for manufacturing flower pots or plates that served as a substrate for cultivating orchids and other epiphytic plants. As a result of this exploitation, as well as the destruction of its native habitat, the samambaiaçu is currently included in the Brazilian Red List of endangered species.

The trade of xaxim is currently forbidden by law in Brazil, so if  you ever find someone selling it somewhere, please, communicate the authorities!

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Schmitt, J., Schneider, P., & Windisch, P. (2009). Crescimento do cáudice e fenologia de Dicksonia sellowiana Hook. (Dicksoniaceae) no sul do Brasil Acta Botanica Brasilica, 23 (1), 283-291 DOI: 10.1590/S0102-33062009000100030

Brazil. Law Nº 9.605/98. Available at: <http://www.planalto.gov.br/ccivil_03/leis/L9605.htm >.

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