11 December 2017

Probably the world's heaviest living organism described in 2017?

Kew scientist Gwilym Lewis describes his involvement in and the process of discovering a new tree species in Brazil, as tall as a 12 storey building and as heavy as a sperm whale!

Gwil Lewis

By Dr Gwilym P Lewis

The Temperate House, RBG Kew

A new discovery

Kew scientists, in collaboration with researchers from Brazil and Canada, have recently published a description of a new tree species from the legume family (Leguminosae or Fabaceae). Dinizia jueirana-facao G.P. Lewis & G.S. Siqueira, discovered in Brazil, grows to a whopping 40 metres with an estimated weight of up to 62 tonnes.

At risk of extinction?

Dinizia jueirana-facao grows in a narrowly restricted area of Atlantic forest in the Brazilian state of Espirito Santo. It is Critically Endangered – we know of only 25 of these trees in the whole world - a fact which helps to explain why such a majestic species has gone undiscovered and scientifically unnamed for so long. If such gigantic species are being described as new to science in the 21st century, just imagine how many smaller organisms are still waiting to be discovered?

Giving a plant a new name

Of the 2,000 new plant species described and published each year by the global botanical community, Kew taxonomists contribute about 200, or around 10 per cent. It’s noteworthy, however, that many of these newly described plants are not based on brand new field discoveries, but rather on new scientific evidence (usually molecular). This could indicate that a plant was originally placed in the wrong genus, or that a large genus needs to be segregated into smaller natural groups or, conversely, smaller genera should be combined. All these taxonomic changes have nomenclatural consequences. Plants (and animals) do sometimes have to change name. Taxonomy is dynamic. On the other hand, several newly described species, and even a few genera, are based on previously unnamed specimens. These have either been recently collected on botanical field expeditions or rediscovered as historical specimens preserved in herbaria.

First discovery

Dinizia jueirana-facao was first collected in flower just over a decade ago by Renato Jesus, then the biodiversity manager of the 22,000 hectare Vale Nature Reserve in Linhares, Espirito Santo, the largest protected area of semi-deciduous forest in eastern Brazil.

I have worked on legumes for many years, and so Renato sent a specimen to Kew for me to analyse, with the original suggestion that the tree perhaps belonged to the legume genus Parkia. It apparently had not flowered before, in the 27 years that Renato had been based at Vale. Was the specimen reaching maturity or did it have an unpredictable phenology? (i.e., the flowering and fruiting times are not regular or annual). No one knew. From a detailed study of the flowers at Kew, it was soon evident that the tree was not a Parkia, but it was also unclear as to which genus it belonged in. So began the process of gathering more data. The following year, fruits were sent from Brazil to Kew. These are large woody pods, nearly half a metre long, and look very like the leathery sheath or scabbard of a machete.

Detailed investigation included DNA analysis

Dr Anne Bruneau in Montreal then carried out a DNA analysis of some leaflets and the new tree was shown to be closely related to the relatively widespread Amazonian legume Dinizia excelsa Ducke, another canopy-emergent tree that reaches up to 60 metres in height. Morphological studies at Kew confirmed the close relationship of the new species to Dinizia excelsa. Dr Hannah Banks, a pollen specialist at Kew, analysed the pollen of the new species. She found that the new species produces smooth, single pollen grains, unlike the pollen of D. excelsa which has knobbly pollen aggregated into tetrads (groups of four grains), suggestive of a different pollination system. Our Brazilian colleague, Geovane Siqueira, sent new observations and numerous photographs of the living tree. All this accumulated information strongly supported the molecular finding that the species is, indeed, a second species of Dinizia, albeit geographically disjunct from its Amazonia sister species first described nearly 100 years earlier.

Choosing a new name

The species name selected for the new Dinizia is taken directly from the local name for the tree, “jueirana-facão”, where facão is the Portuguese for a large knife or machete and alludes to the scabbard-like fruits. Providing this magnificent species with a scientific name will ensure it can be appropriately recorded and help to highlight its threatened status, hopefully resulting in the long term conservation of both the tree and the habitat in which it grows.

Reference

Lewis, G.P., Siqueira, G.S., Banks, H. & Bruneau, A. (2017). The majestic canopy-emergent genus Dinizia(Leguminosae: Caesalpinioideae), including a new species endemic to the Brazilian state of Espirito Santo. Kew Bulletin 72: 48. Published online: 06 October 2017. DOI 10.1007/S12225-017-9720-7.

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