RANGE EXTENSION AND TAXONOMIC NOTES ON Mastixia nimalii IN RATHNAPURA DISTRICT, SRI LANKA

Abstract

The genus Mastixia of the family Nyssaceae is represented by five species in Sri Lanka, including three endemics. M. congylos and M. nimalii are the most recent additions to this genus which are lesser-known species. Extensive floristic surveys were carried out under the Endana biodiversity corridor project, with transects (100 m × 5 m) being demarcated in the Walankanda forest reserve along the elevation gradient. A checklist of the flora in different habitats was recorded and geotagged. M. nimalii; is a rare, endemic, and critically endangered species from Walankanda Forest Reserve of Sinharaja Forest Range. For the first time, another population was observed in Kiribathgala forest reserve near Pelmadulla, Rathnapura. The survey differentiated M. nimalii from the sympatrically occurring M. tetrandra even in sterile conditions in the field, which was not documented before. M. nimalii can be differentiated from the latter by having leaves obovate to oblanceolate (vs. oblanceolate to oblong-oblanceolate), 7 – 14 × 4 – 6 cm (vs. 5 – 10 × 2 – 4 cm), apex acute to lanceolate, base cuneate (vs apex acute, base attenuate), petiole 1.5 – 4 cm (vs. 1.5 – 3), vans 4 – 7 pairs (vs. 4 – 6 pairs). Herbarium specimens were prepared from the collected samples and are to be deposited in the National Herbarium, Peradeniya. Further two distinct micro-habitat conditions were identified for each species. M. nimalii was found in riverine habitats, with branches facing the sunlight, suggesting it is the true Diya-thaliya species, as its vernacular name indicates its close association with water. In contrast, M. tetrandra was found inhabiting higher ground areas. These new records expand the known range of M. nimalii, which was previously reported from a few locations in Sinharaja forest. In the endane threatened plant nursery, a few saplings of M. nimalii are ready for in-situ and ex-situ conservation. These records highlight the value of biodiversity in Walankanda, and Kiribathgala forest reserves for conservation and need for future research on taxonomy within this globally recognized biodiversity hotspot.