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The Exotic Rainforest
Plants in the Exotic Rainforest Collection

Microsorum thailandicum T. Boonkerd & Noot.

Microsorum thailandicum T. Boonkerd & Noot.
Often published as
Microsorium thailandicum 
Previously known as
Microsorum steerii
Blue Fern, Blue Strap Fern, Cobalt Fern, Scarab Fern
An iridescent Cobalt Blue Strap Fern that grows on trees and limestone

Note:  If you located this plant on some websites you may have been confused by the name spelling.  After a good deal of searching I have discovered (January, 2007) the correct genus spelling is "Microsorum".  However, many websites use the spelling "Microsorium" with an "i".  With the assistance of the editors of the University of British Colombia plant web site (UBC) I was directed to the Australian Plant Names Index (APNI).  On that site a quote from a Mr. Bosman clarifies the conflict.  The genus Microsorum was originally published in 1833.  Botanist Dr. Link went on to publish papers in 1841 using both the spelling Microsorum and Microsorium (with an "i") in the same paper.  Since that writing both spellings have been used by botanists to describe the same genus.  Since you can find both genus spellings on numerous scientific sites (TROPICOS, IPNI, ePIC and others) apparently either is acceptable.  But, in the purely technical sense, Microsorum is the correct genus spelling since it was the earlist published.  Two separate genus do not exist.

An unusual ferns in any collection, there is little detailed information to be found in English in any text regarding Microsorum thailandicum (tie-LAND-ee-cum).  Since the botanists who described the fern are Thai the majority of scientific information available is written in that language.  The genus name is confusing since on scientific sites you can find both the genus "Microsorum" and "Microsorium"  containing ferns.  The International Plant Names Index (IPNI), ePIC (Royal Botanic Gardens, Kew, London) and The University of Connecticut have this plant listed as Microsorum thailandicum.   The spelling "Microsorium thailandicum" cannot be verified as a published scientific name through TROPICOS (a service of the Missouri Botanical Garden), IPNI, or ePIC.   Thailand's Dr. Thaweesakdi Boonkerd and Dutch botanist Hans Peter Nooteboom (Noot.) described the species to science in 2001.  Dr. Boonkerd is associated with the Plants of Thailand Research Unit and holds a Ph.D. from the University of Durham in the United Kingdom.  The incorrect spelling (Microsorium thailandicum) has been used repeatedly by numerous websites and sellers on a variety of websites.

Microsorum thailandicum is one of a variety of blue strap ferns known to science.  There are Elaphoglossum which also demonstrate this same coloration.  Although information easily found indicates the color is unique among ferns, commerial grower Jay Vannini indicates, "The plant´s color is not unique...several other Neotropical ferns have it."   A slow growing fern, it is relatively common in southeast Asia but is sometimes considered rare by collectors.  The tips of the fronds may be pointed but are often forked.  Even though the true genus is often confused by plant collectors, strap ferns are always included in the genus Microsorum, not Microsorium by botanists.

Until recently, specimens were often difficult to locate and carried a high price when available.   Due to the popularity of the unusual species it is now often sold by terrarium and vivarium supply stores and the price is reasonable.  Normally, you will receive small immature specimens but if you are willing to wait the several years for the fern to mature the price is more than fair.  However, you can still locate sellers on the internet asking up to $100 for plants of more mature size.  M. thailandicum once commonly brought a very high price, especially on sites such as eBay.  One moderate size eBay specimen attached to a piece of wood brought over $100.00 in the summer of 2006.  Growers in Asia now export the fern in large quantity causing the price to drop. 

Not difficult to grow, Microsorum thailandicum is claimed to be somewhat demanding if you wish to maintain the cobalt blue coloration.  Recent information indicates this is not necessarily true.  According to growers in Thailand, this species, with its 26 to 45cm (10 to 18 inch) fronds, exists in nature in the understory (the zone between the canopy and ground cover plant forms) and appears to prefer both low light and high humidity.  But this fern has sometimes appeared to show even a "sub-understory" light preference.  Recently some growers have had excellent success maintaining the color in very bright light.  Although it will grow in a variety of light conditions, some growers feel if you grow the fern in dim light its semi-glossy fronds which can be forked (see inset left) can turn iridescent cobalt blue with a metallic glow.  Still others experience this blue coloration in very bright light.  This peculiar effect is found a number of fern species in the world and is especially noticed in the case of Microsorum thailandicum when the plant is misted.  If not grown under good conditions when the fronds dry (in some cases) they turn to a less than iridescent green.  If grown well the fern will maintain the metallic blue coloration at all times but is even more beautiful when moist. 

There is however a difference of professional opinion on how much, or how little, light these ferns require to remain blue.  Grower Jay Vaninni offered this explanation, "I have dozens of sporing founders in a warm greenhouse that it lit enough to grow, color and flower thousands of hybrid Neoregelia bromeliads and the ferns look just fine.  By the same token, older plants in my personal collection at the house grown in deep shade also look superb. They do appear to look considerably better when watered with reverse osmosis or rainwater and fertilized with very dilute fish emulsion and/or kelp extract. There are many genera and species of metallic strap-leaf ferns. México, Central and South America are replete with montane Elaphoglossums like this."

The unusual fern species is both epiphytic (a plant that grows on another plant) and lithophitic.  In nature it may grow attached to the sides of trees or fallen tree trunks or on limestone.   Knowledgeable collectors know Microsorum thailandicum as a lithophyte (lith-a-FIT), in Greek meaning "lover of stone".   We now have a group of specimens attached epiphytically to a log reproducing nicely (main photo) and a another group growing lithophytically on limestone (see inset photo right above).   A lithophyte is a plant including some orchids that can grow with its roots attached to stone and derive nourishment primarily from the atmosphere.  Microsorum thailandicum can be induced to grow on limestone if you are willing to spend the time to coax the fern's roots to attach.  If you wish to try this experiment for yourself read our explanation in the last paragraph of this description.

M. thailandicum grows in the limestone hills of the Thailand peninsula as well as Cambodia, Taiwan, southern China and Vietnam.  Our original fern was a gift from plant collector Windy Aubrey in Hawaii.  Windy is considred an expert in the species by many collectors and recommends in to achieve the best color collectors grow the fern in as low light as possible.  Too much light (she insists) and the fronds will stay green even though they will retain some of their iridescence.  Windy grows the fern in dark shade at all times.  Her recommendation is to keep the fern out of direct light as well as in a moist climate due to its need for high humidity.  Jay Vannini has indicated in numerous email he has had just the opposite experience with the blue coloration obvious evenin a greenhouse with very bright light.  Windy also states emphatically this tropical needs a warm climate or a greenhouse since the plant will not tolerate cool temperatures.  

Sori (spore cases) are produced on the undersides of the fronds.  Once released, the spores can produce new ferns provided they attach to a viable source.  A photograph of the sori can be located on the Plants of Thailand Research Unit website.  In addition to reproduction via spores, Microsorum thailandicum reproduces by putting out leading rhizomes once the fern is well established.  The majority of collectors utilize the later method for species reproduction claiming growth from spores is difficult to achieve.  Once a new plant is set off by the parent it can simply be removed by division.

The people of Thailand have a common name for the cobalt blue fern, "waew peek maeng thub".  Translated from Thai that says "shiny as the wings of a scarab beetle".  That observation is apparently how the fern received one of its common names, the Scarab Fern.  Numerous growers and sellers recommend the fern for humid terrariums.  If you elect to grow one in a terrarium or vivarium be sure and protect it from strong overhead light in to enjoy the iridescence.    We keep our dozen specimens near our pond's waterfall where they receive dim light and a regular amount of spray.   However, we bring them indoors for much of the winter (misted daily) because the temp in the atrium can drop to 55 degrees F which is lower than this species will tolerate and still flourish.

Since summer, 2006  we have several of the blue ferns growing on limestone and they are now attached.   The trick to making them attach to limestone is very high humidity and frequent misting.  If you wish to try this yourself you may want to place your plants in a moderately lit vivarium or large decorative apothecary jar with several inches of gravel in the bottom.  Keep the the bottom of the jar filled with water so the gravel is always wet.  This will insure high humidity inside the container.  Place your limestone on top of the gravel with your ferns attached to the stone.  A single drop of Super Glue will insure they not fall out of place.  Suitable pieces of limestone can often be found at pet stores for use in aquariums.  Remove the lid daily and mist the ferns to replenish the air and moisture.  Keep a lid on the vivarium or jar to hold in the humidity and store the jar in a dimly lit area of your home.  Within a few months you should see the roots of Microsorum thailandicum begin to attach.  To insure good growth be sure and mist the ferns daily as well as keep the root system packed with damp orchid moss until you are certain the roots are firmly attached.  We often feed the fern with a very dilute orchid fertilizer.

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