An Overview of the Genus Bulbophyllum

An Overview of the Genus Bulbophyllum

Here we see the distribution of different genera in their natural habitat and the ones most often seen in today’s orchid collections. The temperate terrestrials are not shown.

The three genera with the largest number of species are the Pleurothallid alliance in Central and South America, the Dendrobium alliance from India and S.E.Asia, and the genus Bulbophyllum with the largest number of species spread across the tropical and pan-tropical regions of the world. So how did this geographical diversity come about? And why are Bulbophyllum species distributed across the world?

See reference 'Bee dates Orchids back to the time of Dinosaurs'. The original publication of this article was in ‘Nature’ the International weekly journal of science’ and was issued in the form of a letter.

Ref: Nature 448, 21 June 2007.1024-1045 (30 August 2007) I; doi: 10.1038 /nature 06039 . Received 17 January 2007; Accepted 21 June 2007.

Members of the research team led by Dr Santiago R. Ramirez of Harvard University were: Dr Barbara Gravendeel of the National Herbarium Nederland, Leiden, The Netherlands; Rodrigo B. Singer of the Depto Botanica, University Rio Grande
Do Sul, Port Alegre, Brasil; Charles R. Marshall & Naomi E. Pearce. Harvard University. U.S.A.

The team’s results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76-84 million years ago) and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T* boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.

* The K/T boundary is a geological signature, usually a thin band, dated to 65.5
million years. K is the traditional abbreviation for the Cretaceous period and T is the abbreviation for the Tertiary period. The boundary marks the end of the Mesozoic era and the beginning of the Cenozoic era and is associated with a major mass extinction.

This shows that the orchid family was fairly young at the time the continents started to separate. So let us look at the time frame and continental drift patterns.

The fragmentation of the super continent began about 200 million years ago. Two major rifts initiated the break-up. The rift zone between North America and Africa generated a northern continental group Laurasia.

Gondwanaland break-up - 65 million years.

The rift that separated the southern land-mass of Gondwanaland sent India in a northern direction and simultaneously split South America and Africa from Australia and the Antarctic. Note the large S.E.Asian land mass.
The South Atlantic emerged as a full fledged ocean and Madagascar had broken away from Africa. India and Australia together with New Guinea can be seen at the bottom right of the map. The northern movement of India resulted in a collision with the land-mass of Asia, from which the Himalayas resulted. Australia and New Guinea continued north and eventually joined with the large Indonesian land-mass. The last Glacial Advance (mini ice-age) ended approx 10,000 years ago, causing sea levels to rise, which led to the formation of the Torres Straits and the separation of New Guinea from the Australian mainland and creating the larger Indonesian islands also hundreds of smaller islands including the Melanesian Islands.

Dr Barbara Gravendeel of the ‘National Herbarium in Leiden, the Netherlands, was on the research team at Harvard.

Her main interest is in molecular phylogenies of predominantly Southeast Asian and European plant groups, with an emphasis on phylogenies at species level.

Her research has shown that phylogenetic* analyses of matK* sequences of the cosmopolitan orchid genus Bulbophyllum suggest that the African/South American species are sister to a clade of Asian species. Preliminary molecular clock estimates suggest that divergence of the Asian species from their African and South American relatives coincides with Gondwana break up, and that India served as a raft transporting Bulbophyllum to Asia, where it subsequently radiated on New Guinea.
Sequences of the nr ITS region indicate that the species radiation of Bulbophyllum on Madagascar (PhD-project G. Fischer) is monophyletic*

*Phylogenetic analyses of matK = analyses of one of the major genes on sequencing information.
*A monophyletic group consist of a single plant or animal together with all of its descendants.

Dr Gravendeels research suggest that the basic genetic requirements for the establishment of the genus Bulbophyllum were in place at the time of the Godwana break-up.

Here we see the five major groups of Bulbophyllum which coincide with the continental drifts. The distribution of these species is by no means even. Some areas are poorly represented and others are incredibly rich in numbers. Some of the species in these five groups have evolved quite separately and show some unique features.
Current estimates put the number of good Bulbophyllum species at over 1900.
So how do we recognise the species from this genus?

The genus can easily be recognised. The plants have a sympodial rhizome, with only the last node swollen into a psuedobulb; new shoots as well as inflorescences arise from one of the nodes immediately below the psuedobulb, never from the top of the psuedobulb; the inflorescence can be one to many flowered, and the lip is more or less mobile, because it is attached to the column-foot by a thin ligament. In the illustration we see the two leading psuedobulbs on the left, one with a new shoot growth and the other with an inflorescence.

A few Bulbophyllum species have two leaves, sections Tripudianthes and Megaclinium from Africa; some deciduous species also have two leaves.

to be continued......

bernabu

Awarded the 'Exceptional post bonus' on the 8th January 2010