Taxonomy and molecular phylogeny of the genus aeschynanthus Jack Gesneriaceae in India

Abstract

The present study in India, unveils the taxonomy and molecular phylogeny of Aeschynanthus Jack – the largest epiphytic genus of the family Gesneriaceae. The genus is commonly called ‘lipstick plants’ or ‘blush-worts’ and is principally distributed in Southeast Asia. Globally about 182 species were recognised and show a strong biogeographical distribution pattern; from the Western Ghats and Sri Lanka to the eastern Himalayas through Southeast Asia to the Solomon Islands by crossing the Wallace’s Line. The study recognized20 Aeschynanthus species in India, and its species diversity seems to be maximum in Northeast India (18 species; 90%) and the remaining two species were found in South India and Andaman and Nicobar Islands respectively. The genus is characterized mainly by the epiphytic habitat, fleshy, opposite leaves, roots originating from nodes, brightly coloured (occasionally green, white, or yellow), tubular corolla, pair wise coherent stamens, long, narrow capsules and hair- like appendaged tiny seedsprone to wind dispersal. An integrative approach including morphology, seed micromorphology, palynology, and molecular studies was made here to sort out existing taxonomic problems within the genus, especially for the Indian taxa. A taxonomic key was prepared, and morphological descriptions included detailed colour photo plates for the easy identification of species and to understand variations within the species. During the study, two new species were described from the study area, and three names were lectotypified. The micromorphological studies of seeds along with molecular data reveal that the existing sectional classification was primarily laid on the seed characters which have low molecular support. The palynological studies revealed that the genus was stenopalynous and had no significance in species delineation. Next to pollen, an additional microstructure produced by stamens called orbicules is reported here for the first time in the genus. For the molecular studies, Sanger sequencing and a newly developed Amplicon sequencing pipeline was used. The analysis includes two nuclear (ITS and ETS) and eight chloroplast markers (trnLF, ndhF, matK, rps16, psbA-trnH, rpl32-trnL, rpl20-rps12, and ndhF-rpl32)and generated 382 sequences. The Parsimony and Bayesian analysis supported the monophyly of the genus and was resolved into two major clades, of which all Indian species nested in Clade I. The analysis supports the current synonymisation of the Sri Lankan taxa A. ceylanicus under the South Indian taxa A. perrottetii as well as earlier synonymisation of A. sikkimensis under A. parviflorus, A. austroyunnanensis under A. micranthus, and A. deleiensisand A. mimetes under A. parasiticus as well as the status of newly described species A. reiekensis. Several ecological adaptations were undertaken by Aeschynanthus species in nature for the establishment, survival, and reproduction, which include tolerance to desiccation, prevention of herbivory, bird pollination syndromes, wind dispersal of seeds, etc., of which the Batesian mimicry and vivipary were reporting for the first time in the genus. The conservation status of all the species was assessed according to the IUCN criteria (Version 16, 2024). Among the 20 species, two species each come under Critically Endangered (CR) and Endangered (EN) categories, thirteen under Least Concern (LC), and three under the Data Deficient (DD) category. Due to its floral and foliage beauty, Aeschynanthus has popularised among gardeners and plant enthusiasts by the recent arrival of many exotic species and hybrids to the country. The Indian native Aeschynanthus species prefers particular climatic conditions and was difficult to establish in a different geographical area. Attempts have been made to conserve the wild germplasm at Calicut University Botanical Garden (CUBG) and is resulted in the establishment of the Western Ghat-Sri Lankan endemic species A. perrottetii.