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Maharashtra’s first endemic tree rediscovered after 180 years at Harishchandragad hill

The trees, located next to a perennial stream, were flanked by rock boulders and had the thick canopy of the semi-evergreen forest of the Kalsubai Harishchandragad Wildlife Sanctuary above them.

August 31, 2021 / 04:04 PM IST

-- In 1887, in a mistake in labelling herbarium sheets, plant species from the northern Western Ghats were misidentified. Recently a team of researchers set out to investigate the 180-year-old puzzle.

-- This investigation led the team to discover an entirely new species, Croton chakrabartyi, and rediscover Croton gibsonianus, a previously misidentified plant species that occurs only in Maharashtra.

-- As per the current study, Croton gibsonianus is the only tree exclusively endemic and restricted to Maharashtra. A population of around 50 trees of Croton gibsonianus survives on the Harishchandragad hill in Maharashtra.

While working on a project to document Maharashtra’s endemic species, researchers from the Naoroji Godrej Centre for Plant Research (NGCPR) came across a unique tree that they had never seen before. After an eight-kilometre trek from Khireshwar to the Harishchandragad Hill in the northern Western Ghats, they saw a small population of 15-feet-high trees with bifarious leaves, where the leaves grow on opposite sides of a branch in two vertical rows.

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The trees, located next to a perennial stream, were flanked by rock boulders and had the thick canopy of the semi-evergreen forest of the Kalsubai Harishchandragad Wildlife Sanctuary above them. Initially, the researchers believed these trees were Croton lawianus, a species described by British botanist J.D. Hooker in 1887. But further studies revealed the species to be Croton gibsonianus, described by another British botanist Joseph Nimmo in 1839, based on the field samples collected by Alexander Gibson, the first Forest Conservator of Bombay Presidency.

Morphological studies, examining literature, and subsequent visits to the Western Ghats in Maharashtra and Karnataka revealed that Joseph Nimmo had described two species in 1839: Croton gibsonianus from Harishchandragad and Croton lawianus from Bhimashankar in the Western Ghats. In 1887, J.D. Hooker had apparently made a mistake in labelling herbarium sheets which led to Croton gibsonianus being mislabelled as Croton lawianus, and an entirely different shrub being labelled as Croton gibsonianus.

“So when people later referred to Croton gibsonianus, which species were they referring to? We set out to answer this question and it led us to solve a 180-year-old puzzle about these species,” shared Mayur Nandikar, NGCPR senior scientist and one of the authors of the journal article that resulted from the research. This investigation led the team to discover an entirely new species, Croton chakrabartyi, which they named after Tapas Chakrabarty, ex-scientist with the Botanical Survey of India, for his contribution to the taxonomy of Indian Croton.

Croton chakrabartyi (the new species) occurs in Karnataka and Kerala, but Croton gibsonianus (the rediscovered species) occurs only in Maharashtra. A population of around 50 trees of Croton gibsonianus survives on the Harishchandragad Hill in Maharashtra, which would mean that this species is critically endangered when assessed as per the IUCN Red List because of its restricted area of occupancy and plausible threat to its habitat from tourism-related activities. For a species to be designated as critically endangered, restricted area of occupancy and threat to habitat are requirements. Croton chakrabartyi, the new species described, does not seem to be under any imminent threat of extinction.

Navendu Page, Scientist-C with the Wildlife Institute of India, said that he has seen and collected Croton chakrabartyi a few times from the Central Western Ghats, but was under the impression that it is Croton gibsonianus because this is what it was described as in regional floras of Karnataka. “This species is not rare, but it has just been misidentified. It is a fairly common understory shrub in the evergreen forests of Uttara Kannada and Shimoga in the Central Western Ghats,” he shared.

The researchers also tried to find Croton lawianus at Bhimashankar Hill and in the Western Ghats in Karnataka, but could not find any tree resembling Nimmo’s description. The taxonomic status of Croton lawianus, which is currently a critically endangered species according to the IUCN Red List, was thus concluded to be ambiguous by the researchers.

Tapas Chakrabarty, ex-scientist with the Botanical Survey of India, whom the new species was named after but who was not associated with the present study, said that this rediscovery is significant because botanists thought that the tree, that is now correctly identified as Croton gibsonianus, was extinct.

“Many botanists continued J.D. Hooker’s mistake and referred to Croton gibsonianus as Croton lawianus. When I worked with the Botanical Survey of India on a project to reassess the plant wealth of India, we continued to follow Hooker’s description and treated the actual Croton gibsonianus as Croton lawianus,” he shared. Chakrabarty’s paper titled A revision of Croton L. (Euphorbiaceae) for Indian subcontinent published in 1997 mentions that “Croton lawianus is very rare and apparently has never been collected during the present century.”

Vinaya Ghate, a retired scientist with the Agharkar Research Institute, Pune, who was also not associated with the present study, shared that 54 endemic tree species are found in Maharashtra. Nandikar added that these 54 tree species are endemic to India but are not exclusively endemic to Maharashtra. “As per our study of the literature and current understanding, Croton gibsonianus is the only tree species that is exclusively endemic and restricted to Maharashtra,” shared Nandikar.

“Maharashtra has a number of tree species endemic to the Western Ghats (WG) which are widely distributed in Central and Southern Western Ghats as well. But there are very few species that are exclusively endemic only to the northern Western Ghats. This species is exceptional because most of the narrow endemic species trees and shrubs of WG are distributed in the Central or Southern Western Ghats,” shared Navendu Page, Scientist-C with the Wildlife Institute of India.

In another visit to the area, the NGCPR researchers found one more individual Croton gibsonianus tree about 50 metres away from the first group of 50 Croton gibsonianus trees. “We estimate that the first group of trees is around 100 years old, based on their growth, habitat, and girth of 40-50 cms,” said Nandikar. “Strangely, we searched for Croton gibsonianus in different patches of Harishchandragad with similar habitats, but we found only this one additional individual. We believe this is because the habitat it needs is very specific. We are planning more visits to ascertain if the tree survives anywhere else on the hill,” added Maniruddin Dhabak, the first author of the research paper.

The researchers found that Croton gibsonianus grows along perennial streams/waterfalls near rock boulders at a particular elevation. “We have not observed any Croton gibsonianus trees downstream. They require elevation, moist semi-evergreen forests, and shade. This habitat is important when we are talking about conservation, so we do not believe that ex-situ conservation of this species is immediately possible,” said Nandikar.

Croton gibsonianus and Croton chakrabartyi are morphologically very dissimilar, which means that they look very different from each other. Croton gibsonianus is a small tree, while Croton chakrabartyi is a shrub. “If you see the habitat and habits of both species, they are very unique and very distinct from each other. They may be each other’s closest relatives but further studies are needed to find out more about their evolution and pollination,” Nandikar added.

Endangered status and need for conservation 

Rushabh Chaudhari, one of the authors of the current research, said that Croton lawianus (the species the researchers have now found to be Croton gibsonianus) was assessed as critically endangered based on its restricted geographic range, single location and continuing decline in area, extent or quality of habitat by the World Conservation Monitoring Centre in 1998. This assessment was done using previously published literature and herbarium specimens, which was permitted under the IUCN, based on available data on its distribution and predicted threats.

Though the population of Croton gibsonianus occurs within a protected area, the researchers still believe conservation efforts are needed to prevent the species from going extinct because the species has a very low area of occupancy. “With our research, the name of the species has changed but its rarity status has remained the same,” shared Chaudhari. Harishchandragad hill being a tourist destination, any widening of paths/roads near the Croton gibsonianus population could pose a threat to its habitat and to its existence, warned Nandikar.

To ensure that the species is conserved, in situ conservation plans are being considered by the researchers. “The species is habitat-specific and we cannot create such unique and beautiful habitats in a botanical garden, but we can do it in the biosphere reserves of wildlife sanctuaries where such habitats already exist. Some ghat areas where there are perennial springs could work for in-situ conservation,” shared Nandikar.

The name of the species matters for botanical nomenclature and correcting cases of mistaken identity is very important, said Tapas Chakrabarty. “As per the botanical nomenclature, there have to be preserved herbarium specimens or preserved botanical drawings which serve as the ‘type’ or standard point of reference of botanical nomenclature. The International Code of Botanical Nomenclature must be followed in case of new species,” said Chakrabarty.

This story was first published on Mongabay, click here to access it.
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