Pteridospermales (Cycadofilicales): An Overview

The Pteridospermales or Cycadofilicales are characteristic gymnospermous plants that bore fern-like foliage, which in turn bore seeds that were unprotected. Hence, they are known as seed ferns.

Pteridospermales is a very large order that includes a heterogeneous assemblage of tree-like organisms. The plants lived through the Carboniferous period, reached their climax, and became extinct in the Jurassic period of the Mesozoic era.

Characteristics of Pteridospermales

• Plants possessed erect, slender, or weak stems with large frond-like leaves.
• Primary xylem was in the form of a solid or medullated protostele and was usually mesarch, rarely exarch.
• Secondary wood was monoxylic.
• Tracheids of secondary wood had multiseriate-bordered pits on their radial walls.
• The leaves were large, fern-like, and pinnately compound. They were arranged spirally at the apex of the stem.
• The leaves of all types were covered by a resistant cuticle.
• Microsporangia were exanulate and, sometimes, grouped into synangia.
• Megasporophyll were like foliage leaves.
• The integument was vascularized.
• The nucellus was also vascularized in some ovules.
• No pollen tubes were present in the pollen grains.
• The pollen grains (megaspores) may be monolete or trilete.
• Megaspore was surrounded by a thick wall.
• The seeds were not borne on inflorescence or cones.
• Seeds had a considerable resemblance to those of present-day cycads.

Classification of Pteridospermales

Arnold (1948) divided Pteridospermales into three families. Viz-

1. Lyginopteridaceae
2. Medullosaceae
3. Calamopityaceae

Sporne (1974) divided it into the following seven families:

1. Lyginopteridaceae
2. Medullosaceae
3. Calamopityaceae
4. Glossopteridaceae
5. Peltaspermaceae
6. Corystospermaceae
7. Caytoniaceae