FERN

The group – Pteridophyta consists of ferns and club-mosses. Dryopteris is a fern. It is seen growing in large number as epiphytes on oil palm trees. Dryopteris has a tuft of strong adventitious roots, a short unbranching stem and leaves in the form of fronds.

The leaf is a frond made up of a main axis the rachis, the leaflet called pinna and the sub division of the leaflet called pinnule. It is like the compound leaf of a flowering plant.

Unlike the bryophyte, the vegetative plant is the sporophyte which reproduces asexually by spores. In Dryopteris as in most Pteridophyta, spores are borne on the under surface (abaxial surface) of the leaves. Many spores are produced in a single sporangium. Many sporangia are organized into a sorus with or without a cover or indusium.

When the spores mature, the indusium breaks open to expose the sporangia. Each sporangium breaks open on drying and the spores fall off. The spores are dispersed by wind. In Dryopteris, the spores are (homosporous) all the same. Each germinates into a bisexual prothallus. The prothallus is a separate plant on its own. It is chlorophyllous and photosynthetic. It has both male and female reproductive organs. It repro-duces sexually by gametes. The prothallus is flattened and shield-like in structure. It is seen growing on the stem of oil palm trees in the rainy season.

The antherozoids (male gametes) are ciliated and swim in the film of water between the prothallus and the substratum. One antherozoid enters the archegonium and fuses with the egg.

A zygote develops within the archegonium in the prothallus. The zygote germinates into the sporophyte sending the young root into the substratum and the young shoot above the prothallus.

Germinating young sporophyte on a prothallus

As the sporophyte grows older, the prothallus (gametophyte) breaks down and rots away.