Dialium travancoricum Bourd., an evergreen tree of the family Leguminosae (Dialioideae), endemic to the southern Western Ghats of Kerala, India, is the sole representative of its genus in India. This species was first collected by T.F. Bourdillon in 1898 in Ponmudi, Thiruvananthapuram district, and later from Aryankavu, Kollam district. The species had not been recorded since then and there was no ex situ conservation collection. The species was categorized as Indeterminate and Possibly Extinct in the Red Data Book of Indian Plants in 1990, categorized as Critically Endangered on the IUCN Red List in 1998, and included in the national priority list of threatened plants in 2005.
While surveying for the rare tree Buchanania barberi in Ponmudi and Aryankavu during August 2019–March 2021, with support from The Mohamed Bin Zayed Species Conservation Fund (grant no. 180519970), we located one flowering individual of D. travancoricum in the evergreen tropical rainforest of Ponmudi, at 490 m altitude. We did not locate the species in Aryankavu. We conclude that the global population is small, with < 50 mature individuals in an area of < 1 km2, and recommend that it continues to be categorized as Critically Endangered, but based on criteria B2ab(iii,v);D. Information from local people suggested that the potential threats to the species are: (1) habitat destruction caused by road construction, (2) increasing tourism in Ponmudi (a hill station), (3) low fruit set despite a high level of flowering, (4) few seedlings, and (5) former consumption of its fruits as a tamarind substitute (it is known locally as hill tamarind or Malampuli).
Action is required for the protection of this rare species. At Jawaharlal Nehru Tropical Botanic Garden and Research Institute seed germination and seedling establishment experiments are being carried out on seeds collected from Ponmudi, and trials are underway to raise seedlings using tissue culture. Further surveys across Ponmudi and Aryankavu are required, to determine if there are more individuals and, if so, to collect additional seeds for ex situ conservation.
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