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The genus Coryanthes

For 20 years now I have been working with Coryanthes. My first contact with this bizarre genus was in the Botanical Garden of Heidelberg where I worked as an orchid gardener. Mr. Seeger the head gardener and I were so excited by the fantastic flowers that we decided to build up a Coryanthes collection. On various expeditions to the Neotropis we collected nearly all known species. In the collections of Heidelberg and Munich Botanical Gardens we now have about 38 species in cultivation.

Coryanthes species
Images of Coryanthes
Images of the subtribe Stanhopeinae

Introduction

The genus Coryanthes was founded by Sir William Hooker at the beginning of the last century. Schlechter already recognized 16 species in his revision of the genus. Only two of them (C. bungerothii Rolfe, C. wolfii Lehmann) represented synonyms caused by the closed herbarium of Reichenbach. Another problem caused by the closure of the Reichenbach herbarium is depicted in the drawing of Barbosa Rodrigues from Brazil, two different species of the two different sections were united on one single inflorescence and titled as C. biflora. This epithet means two flowered Coryanthes, perhaps referring to the difference of the two flowers. We have no information about the genesis of this drawing, but it seems clear that this inflorescence is an artificial product. Rolfe noted this on the sheet and later Hoehne described one of the species as Coryanthes rodriguesii, but he forgot to give a latin description, so the name C. rodriguesii is invalid.

The distribution of the genus Coryanthes extends from Mexico in the North to Bolivia and Brazil in the South. The plants prefer habitats with high humidity and high temperatures, they were often encountered near rivers in primary forrest. They grow in altitudes from sea level up to 1200 m.

All the Coryanthes species are found growing in so called ant-gardens. The ants and the plants have what is known as a symbiotic relationship, that is, they benefit from each other. The plants offer nectar in extrafloral nectaries and provide a base for nest construction with their root system, while the ants defend the plants against herbivores and additionally fertilise them with vertebrate faeces. The abundant provision of nutrients allow the plants to grow very rapidly. Raised from seed Coryanthes plants need about 2 to 3 years to flower. Seed ripening is also very quick. All the species need 60 to 70 days to produce around 600,000 seeds.

Extrafloral nectaries attract the ants to the new shoots, the most vulnerable parts of the Coryanthes plant. New shoots do not contain bitter tasting compounds which repel predators. In this way the aggressive, biting ants are positioned exactly where the plant is most in need of defence.

Reproduction is improved by the protection of the flower buds. Nectaries on the outer side of the sepals are frequently visited by the symbiosis partners who defend their sugar source with a vehemence.

In the last century Coryanthes were thought to be pollinated by hummingbirds. The pollination biologist Delpino designed a special type of pollination syndrome for this genus. Kolibris are known as visitors to the liquid filled buckets but are unable to reach pollinarium and stigma.

Coryanthes species are pollinated exclusively by fragrance collecting male euglossine bees. The bees are attracted by the characteristic aroma of the flower and try to come closer to the fragrance source, the osmophor hidden below the hypochile. The bees get more and more excited, lose their foothold and fall in the liquid filled bucket. Their wings are now wet and they cannot escape by flight, the walls of the bucket are slippery so the only way out is to climb up the callus which to the bee is the equivalent of dry ground. The bee is now below the column and exits by squeezing past the lip. Struggling to escape the bee first passes the stigma and then the pollinarium. When a pollinarium carrying bee passes the stigma the pollinia are scraped off by a special structure of the rostellum. Afterwards the insect receives a new pollinarium, if available. The passage lasts about half an hour when the flower still possesses its pollinarium, when no pollinarium is there the visit is much shorter. The impression left by the visit to the flower is so negative that the bee does not try it again for some time. In this way an effective mechanism to avoid self pollination has evolved.

To collect fragrances the male euglossine bee wipes them off the osmophor surface with special brushes on his fore legs. When they are saturated the bee flies off and scrapes them, with the help of the middle pair of legs, into the inflated hind legs for storage. If the fragrance compounds are excreted by the flower in cristalline form the bees disolve them first with gland secretions and wipe them off afterwards. Until now we do not know why the male bees collect the fragrances, but we are sure that they need them for reproduction.

The pollinators of the different Coryanthes species fit exactly to the size of the tunnel formed by the lip and the column. A bee which is too big cannot pass through the flower and drowns in the liquid filled bucket while a bee which is too small may pass through the flower without effecting pollination. The characteristic aroma of the flowers is responsible that such accidents do not happen and that only the appropriate pollinator is attracted.

In spite of the very close relationship between the orchid and the pollinating bee species, orchids of different genera can be pollinated by one single bee species. This is facilitated by a different position of the orchid pollinarium on the bees body. A bee with pollinaria of Coryanthes and Gongora can pollinate both without effecting crossbreeding. Here the Coryanthes pollinarium points forward while the Gongora pollinarium points backward. Both genera can possess the same fragrance composition, crossbreeding is here avoided by different pollinarium position on the bees body.

Chromatograms of the fragrances of different Coryanthes species show different fragrance compositions. Different bee species are attracted by the respective fragrances, resulting in a very effective isolation mechanism between the species. So the same habitat can be occupied by more than one Coryanthes species without the risk of interbreeding.

The fragrance compounds involved in the "perfume-flower-syndrome" show a simple chemical structure. Terpenes as well as esters are the main compounds. Many of them are well known like cineole in "Vick Vaporub" or methylsalicylate found in some chewing gums.

The genus Coryanthes can be divided into two sections, the section Coryanthes with a smooth mesochile and the section Lamellunguis with a mesochile bearing transversal lamellae or wart like protuberances.