Diversity of Nypa in the Indian subcontinent: Late Cretaceous to Recent

Abstract

Nypa, a monotypic genus of the family Arecaceae, is restricted to the mangrove ecosystem on the tropical coasts of south-east Asia and Australia. In the Indian subcontinent, it grows in Gangetic delta, Andamans and Sri Lanka. The fossil remains including fruits, roots, cuticles and pollen assigned to this genus are well-documented since Late Cretaceous to Pliocene having pantropical distribution. Fruits cf. Nypa, described under several species on the basis of size and shape variations, are now considered a single species because of wide variations in the living plants. Similarly, the roots and cuticle described show affinity with modern Nypa fruticans. Fossil pollen attributed to the pollen of Nypa is referred to Spinizonocolpites Muller 1968 which is represented by 13 species in India. Out of them, 8 species and two specimens are found to be distinct by virtue of their morphological differences in exine and its sculptural type. Only one fossil species is similar, if not identical, to the pollen of Nypa fruticans; other fossil pollen shows considerable morphological variations but the pollen of extant Nypa does not show such variations. This suggests that Nypa fruticans is a relict species of a large group of early Nypa-complex prevalent in India during Late Cretaceous to Eocene but more diverse during Palaeocene. In the Palaeocene sediments of north-eastern India Spinizonocolpites is an important element both in terms of diversity and preservation and probably the richest record in the world. After Eocene, the fossil pollen records are represented by only one species - S. prominatus showing similarity with the pollen of Nypa fruticans. Thus it seems that the early Nypa-complex may have experimented with the various habitats and due to other successful competitors may have perished except for its living counterpart which occupied only the mangrove habitat.