In this article we will discuss about the origin and affinities of glossopteridae.
Origin of Glossopteridae:
Brongniart, in 1828, established the genus Glossopteris for leaves, believed to be ferns from the Paleozoic and early Triassic of the Southern Hemisphere. These were simple and entire and as the name suggest tongue-shaped or spathulate to ovate or linear-lanceolate in outline and either sessile or shortly and distinctly petiolate. They had a conspicuous midrib from which arise lateral and a network of small anastomosing veins.
The leaves were often borne on characteristic rhizome-like stems, Vertebraria, bearing secondary wood with multiseriate pitted tracheids. Vascular skeleton appears to be constructed of several plates of vascular tissue radiating from a common centre.
Cuticular studies have suggested that these represent seed plants. This is supported by the finding of unique types of reproductive organs, of varied morphological nature; one of which (Scutum Leslium Plumstead) has actually yielded seed-like structures.
Generally stalked reproductive structures of Glossopteris are either oval, round or lanceolate in shape and in most cases show a central seed- bearing portion surrounded by a marginal flap. Knowledge regarding the nature of the reproductive structures bearing pollen sacs is still lacking.
It has been suggested by some that the Glossopteris are to be included under Pteridospermae and a new class Glossopteridae should be created for them. They occur in various continents in the Southern Hemisphere previously connected together in the Gondwanaland. They are abundant in the Raniganj and Jharia coalfields.
Affinity of Glossopteridae:
As the name indicates, the order shows resemblance on the onehand with Filicales and on the other hand with Cycads.
(a) Affinities with Ferns:
1. They are ferns-bearing seeds.
2. In micro-sporangiate structure they can hardly be regarded above the level of ferns. These structures have resemblance with those of the marattiaceous ferns and some of the Botryopteridium.
3. Sporophylls are little modified from vegetative foliage.
4. The general form of the foliage is fern-like.
5. The vascular anatomy has got similarity except in the secondary growth in Cycadofilicales.
(b) Affinities with Cycads:
1. They are Cycads without strobili. Though the primary stele of Heterangium or Medullosa resemble ferns yet when the stem structure is viewed, as a whole, it is decidedly Cycad-like.
2. Structure of petiole, stem and the seeds of the members of medullosae are closer to the Cycads.
3. The relationship with Bennettitales and Cycadales shows evidences that all the three have been grouped into one division Cycadophyta.
(c) Affinities with Higher Gymnosperms:
There is not much relationship with the Cordaitales, Coniferales and Gnetales. Although there is a suggestive connection between Calamopityaceae and Pityaceae particularly in the wood characters.