Glossopteridales: An intricate group of plants

Abstract

The earliest representative of Glossopteridales is known by the leaves discovered from India and Australia (Brongniart 1822–28) under the genus Glossopteris as Glossopteris browniana var. australasica and Glossopteris browniana var. indica. Later discovery proved the presence of similar leaves in all the Gondwana continents, i.e. India, Australia, Antarctica, South America and Africa ranging from late Carboniferous to entire span of Permian to early Triassic. Such distribution pattern provides major evidence for the theory of continental drift. As a unified character, these tongue–shaped leaves show reticulate venation pattern and a midrib. Later, non reticulate and non midrib leaves were also considered as ally due to their close association with the leaves of Glossopteris and together they are assigned to Glossopteridales consisting of different genera, e.g. Gangamopteris, Rubidgea, Euryphyllum, Palaeovittaria, Maheshwariphyllum, Rhabdotaenia, Sagittophyllum, Pteronilssonia, Surangephyllum, Gondwanophyllites, Laceyphyllum, Belemnopteris, etc. Later, cuticular study, discovery of fertile structures in attachment with leaves increased the number of species. In addition, permineralized leaf fossils with anatomical features have also been described under new species of Glossopteris. Fertile structures of glossopterids are mainly discovered in attachment with leaves or in attachment with scale leaves or bracts. Leaf borne fertile structures are known by multiovulate ovule/ seed bearing organ with or without stalk, e.g. Ottokaria, Dictyopteridium, Scutum, Senotheca, Cistella, Plumsteadiostrobus, Jambadostrobu, Lanceolatus, Vanus, Pluma, Hirsutum, etc. Scales or bracts showing branched and unbranched cupulate organs are other mode of fertile structures, e.g. Lidgettonia, Partha, Denkania, Bifariala, Nogoa, Gladiopomum, Rusangea, Rigbya, Mooia, etc. Distinct seed bearing Arberia, Dolianitia–type of fructifications, Eretmonia, Glossotheca type of sporangia bearing scale leaf or bract, Arberiella–sporangial mass and a variety of dispersed seeds are also accredited to glossopterids. Ironically, leaves and fructifications have not yet been found in attachment with stem, however, fossil woods with araucariod pits, e.g. Dadoxylon/ Araucarioxylon found in alliance demonstrate their affiliation with glossopterids. Vertebraria–axes commonly observed in the sediments exemplify the rooting behaviour of the glossopterids. Combination of different types of leaves consisting of more than 130 species under closely allied genera, thirty five to forty types of fructifications grouped under multiovulate and branched types together with seed–bearing structures, varied type of morphological, cuticular and structural features amply demonstrate that Glossopteridales had sundry approach for development, endurance and evolution and in all likeness represent different taxonomic characteristics.