Saturday, 15 August 2015

Gastrodia madagascariensis: A (not so) new species of parasitic Orchid from Madagascar.


The German botanist Rudolf Schlechter published Orchidaceae Perrierianae, a description of all then known species of Orchids from Madagascar, including 332 new species based upon material supplied by the French plant-collector Joseph Marie Henry Alfred Perrier de la Bâthie. One specimen mentioned in this volume was a leafless orchid lacking chlorophyll, which Schlester assigned to the genus Gastrodia, but did not assign to a specific genus due to the limited material available. Unfortunately Schlechter died shortly after this volume was published, leaving much material supplied by Perrier de la Bâthie undescribed. In 1939 and 1942 Perrier de la Bâthie published his own description of this material in the two volume work Flore de Madagascar, including a description of chlorophyll-less Orchid under the name Gastrodia madagascariensis. However Perrier de la Bâthie’s description was in French, in breach of then requirements of the International Code of Nomenclature which required descriptions in Latin, and much of the material was subsequently destroyed the bombing of the Berlin Herbarium in March 1943, leaving the status of Perrier de la Bâthie’s Orchid in limbo.

In a paper published in the journal Phytotaxa on 28 July 2015, Florent Martos, Steven Johnson and Benny Bytebier of the School of Life Sciences at the University of KwaZulu-Natal, describe new specimens of a parasitic Orchid from Madagascar, which they believe to be the same species as Perrier de la Bâthie’s Orchid, and formally redescribe this as Gastrodia madagascariensis.

Gastrodia madagascariensis is a slender leafless Orchid reaching 100-300 mm in height, with a dark brown or blackish stem. It produces 3-12 light or reddish brown in colour, darkening to blackish at the apex, with yellow-orange and emerald green markings. It was growing as an understory plant in the humid evergreen Ambodiriana Forest, at altitudes below 200 m.

Gastrodia madagascariensis. (A) Growing plant; note the dark colour of the peduncle contrasting with the whitish pedicels, and the dark colour of the perianth tube at the apex. (B) Open flower, front view; note the perianth tube spreading towards the apex, and the reddish brown (bottom half) and light brown (top half) colour of the perianth tube on the inner surface. (C). Open flower, three quarter view; note the emerald green colour of the lip tip and of two tubercular calli borne on the column-foot (also seen on B). D. Dehiscent capsules borne on elongated fruiting pedicels. (E) Fusiform rhizome with fine adventitious roots. A Charbouillot and Jean-Michel Hervouet in Martos et al. (2015).

All terrestrial plants survive by forming symbiotic relationships with mycorrhizal fungi, which absorb minerals and nutrients from the soil and pass them on to the plant roots in return for sugars produced by photosynthesis. However in a few groups of plants some members have developed the ability to live parasitically upon these fungi, absorbing both minerals and sugars produced by other plants through their roots. These plants do not produce chlorophyll or photosynthesize themselves.

In 1953 Victor Summerhayes suggested that Perrier de la Bâthie’s Orchid should be placed in the genus Didymoplexis, due to its elongated fruiting pedicles, and though since this time other members of the genus Gastrodia have been found with elongated fruiting pedicles, it has not been possible to resolve the precise generic position of Perrier de la Bâthie’s Orchid with the limited material available. Perrier de la Bâthie collected his specimens in 1912, and no further specimens of either genus were discovered on Madagascar until 2005, when specimens of Didymoplexis were found growing on the island; since this time two new members of that genus have been described from Madagascar, and one southern African species has also been found on the island, and while none of these could be connected directly to Perrier de la Bâthie’s Orchid, they did lend support to the idea that this could also be a member of the genus Didymoplexis.

The Orchids discovered by Martos et al. were found growing in Ambodiriana Forest near Manompana, near to the river Manompana and its tributaries. This is less than 10 km from the location given by Perrier de la Bâthie for his Orchid, in the basin of the river Fandrarazana. Martos et al.’s Orchid flowers in the cooler dryer season (the forests of east Madagascar do not have a dry cool or dry season) in July to August and produces fruits in August to September, while Perrier de la Bâthie collected his Orchid’s in September, when they were in fruit. It cannot be asserted conclusively that Martos et al.’s and Perrier de la Bâthie’s Orchids are the same species without DNA barcoding, however this would involve destroying the very limited material remaining from Perrier de la Bâthie’s Orchid, and could not be guaranteed to produce results anyway, as this material is over 100 years old and current DNA barcoding techniques are notoriously unreliable for Orchid’s at the best of times.

Map of Madagascar showing the distribution of the various observations of Gastrodieae on the island. Didymoplexis avaratraensis and Didymoplexis recurvata, both endemic to Madagascar, co-occur in the northern province of Antsiranana, in evergreen wet forest at mid elevation. Didymoplexis verrucosa, also known from South Africa, was recently photographed in the western province of Mahajanga, in deciduous seasonally dry forest. Gastrodia madagascariensis occurs in the eastern province of Toamasina opposite the island Nosy Boraha, in evergreen wet forest at low elevation. Filled triangles: flowers observed. Open triangle: only fruits observed. Martos et al. (2015).

The Ambodiriana Forest is a protected forest controlled by the Association de Défense de la Forêt d’Ambodiriana, however like other forests of east Madagascar, protected or otherwise, it is considered vulnerable to slash-and-burn agriculture, with fields currently reaching within 2 km of the forest’s border. All of the known plants of Gastrodia madagascariensis  were found growing within an area of 2.25 km2, with less than 50 plants observed in the 2013 growing season. It is also likely that the plant needs to be associated with particular mycorrhizal fungi for carbon-uptake. For this reason Martos et al. recommend that it be listed as Critically Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.

Inflorescence of Gastrodia madagascariensis. A Charbouillot in Martos et al. (2015).

See also…

Catasetum telespirense: A new species of epiphytic Orchid from the southern Brazilian Amazon.
In 2011-2012 a series of series of rescue expeditions recovered and relocated around 105 000 epiphytic plants (plants which live on other plants, typically...


Balanophora coralliformis: A new species of parasitic plant from Luzon Island in the Philippines.
Balanophoras, Balanophoraceae, are parasitic plants related to Sandlewoods and Mistletoes found in tropical and temperate...

A new species of parasitic Orchid from Takeshima Island, Japan.
Orchids of the genus Gastrodia are found across temperate and tropical Asia, Oceania and Madagascar. They are mycoheterotrophs; parasitic plants which obtain nutrients and sugars from Mycorrhizal Fungi (Fungi which normally form symbiotic...


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