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Derrick

Caularthron bilamellatum

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Derrick   

Caularthron bilamellatum (Rchb. f.) Richard Evans Schultes published in Botanical Museum Leaflets 18(3) 1958.  Basionym Epidendrum bilamellatum Heinrich Gustav Reichenbach published in Annales Botanices Systematicae 6, 1862.  Synonyms Diacrium bigibberosum, D. bilamellatum, D. indivisum, D. venezuelanum.

  Etymology of bilamellatum is from the Latin adjective bilamellatus, which means having two edges - here referring to the shape of the callus that in this context is a stiff protuberance on the lip of an orchid flower.  A common incorrect spelling of “bimellatum” in much of the Caularthron literature originates from a typographical error.

  Description, Rhizomes with fusiform (tapering at each end) to cylindric, hollow pseudobulbs that reach 25 cm tall covered with papery bracts.  One to four lanceolate (lance-shaped) 20x3.5 cm sessile (stalk less), glossy, glabrous, fleshy leaves arise from the apex of each pseudobulb followed by erect inflorescences reaching to 30 cm in length.  These bear 2-20 showy white flowers, sometimes flushed pink.  Flowers are frequently cleistogamous (self-fertilising) and the flowers do not open fully or only briefly, which is perhaps why Fisher found that the presence of ants did not affect its fruit set.  (Fisher & Zimmerman 1988.) Dolichoderus bispinosus, a very aggressive species is one reported inhabitant, See www.antweb.org. Each pseudobulb has an entrance for ants at its base and pseudobulbs are nearly always colonized in nature. Indeed, a study in Panama found that 85% of plants contained resident ants from among 11 possible local species.  Therefore, this is a generalised ant/plant symbiotic mutualism.  (Fisher & Zimmerman 1988.)

  Habitats/Range: Plants are uncommon in much of their wide range especially in northern Central America where they tend to be particularly uncommon.  In southern Mexico, Belize and south-eastern Guatemala they occur in swamp and wet forests at elevations up to 150 m. (500 ft.)  They are also recorded in Honduras and El Salvador and further south in Nicaragua they inhabit evergreen forests, open pastures, and even fence rows from sea level to 500 m. (1650 ft.)  Further south again in Costa Rica they become abundant in dry forests on both the Pacific and Caribbean sides of the dividing ranges.  In Panama at the southernmost end of Central America, they are reported near Chiriquí Lagoon and in open woods east of Panama City as well as in several other locations.  In South America, they are common throughout northern Venezuela such as in the Caracas valley where one presumes they may grow at somewhat higher altitudes.  A dwarf form with smaller rose pink, cleistogamous flowers hails from here.  In Ecuador, they are found in Esmeraldas Province near the northwest coast in dry tropical forests below 50 m (150 ft.)  The species is also native to Colombia, Guiana, Brazil and the islands of Trinidad/Tobago where it meets Caularthron bicornutum.  In Trinidad, it grows on large shade trees in populated areas of the island’s plains.

  Ecology: I quote from an informative research abstract that confirms ant-derived nutrient uptake through the domatia walls of Caularthron.

"Background and Aims. Mutualistic ant-plant associations are common in a variety of plant families. Some myrmecophytic plants, such as the epiphytic orchid Caularthron bilamellatum, actively form hollow structures that provide nesting space for ants (myrmecodomatia), despite a substantial loss of water-storage tissue. This study aimed at assessing the ability of the orchid to take up nitrogen (N.) from ant-inhabited domatia as possible trade-off for the sacrifice of potential water storage capacity.

Methods. Nitrogen uptake capabilities and uptake kinetics of (15) N-labelled compounds (N. H. (4) (+), urea and l -glutamine) were studied in field-grown Caularthron bilamellatum plants in a tropical moist forest in Panama.  Plants were either labelled directly, by injecting substrates into the hollow pseudobulbs or indirectly, by labeling of the associated ants in situ.

Key Results Caularthron bilamellatum plants were able to take up all tested inorganic and organic nitrogen forms through the inner surface of the pseudobulbs. Uptake of N. H.(4)(+) and glutamine followed Michaelis-Menten kinetics, but urea uptake was not saturable up to 2 mm. (15)N-labelled compounds were rapidly trans-located and incorporated into vegetative and reproductive structures.

By labeling ants with (15) N in situ, we were able to prove that ants transfer N to the plants under field conditions.  (Substrates in chemistry are defined as (chemical) reactants that are consumed during catalytic or enzymatic reactions.)

Conclusions. Based on (15) N labeling experiments we were able to demonstrate, for the first time, that a myrmecophytic orchid is capable of actively acquiring different forms of nitrogen from its domatia and that nutrient flux from ants to plants does indeed occur under natural conditions. This suggests that beyond anti-herbivore protection host plants benefit from ants by taking up nitrogen derived from ant debris." (Gegenbauer et al. 2012.)

A claim to be first is debatable.  See Myrmecophila (as Schomburgkia) tibicinis (Rico-Gray, et al. 1989.)

Can anyone supply a quality image.

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Derrick:

 

This species is rather common in coastal rainforest of NE Guatemala, but unfortunately the populations there appear to be entirely cleistogamous. In my experience plants from this region do not open flower buds even to gap the sepals, although the unopened buds change from green to pure white immediately prior to self-pollinating. Unlike the three Myrmecophila spp. and their hybrid swarm that also occur in the general vicinity, I have only found C. bilamellatum growing under bright, semi-shady conditions under broadleaf canopy rather than exposed at edge of riparian and flood forest and on red mangrove (Rhizophora mangle). They are rare on the Pacific versant, and I am not aware of anyone finding them on the northern edge of their range adjacent the Guatemala-Chiapas border in many years.

 

They flower during the height of the dry season in Central America. A friend who is a professional orchid guide and photographer sent me a photo of a plant in full flower on Pacific versant of Nicaragua on April 03 but I don't have permission to post. I will ask him if he wants to add images to this thread. Plants in this area are not cleistogamous and are somewhat showy, but are significantly smaller than the far more popular hort subject from South America, C. bicornutum.

 

Decent distance shot of plant habit at sea level in NW Panamá is linked here: http://www.orchidspecies.com/orphotodir/caularthrobilammelat.jpg

 

...or Google this species at IOSPE and click on link provided there.

 

J

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