Pteridophyta

Pteridophyta takes its name from the Greek pteron (feather) and phyton (plant), reflecting the feather-like (pinnate) form of many of its leaves. The group has about 400 genera and 11,000 species, and the late Paleozoic era is regarded as the 'age of Pteridophytes'.

Evolutionary significance. Pteridophytes were, evolutionarily, the first vascular and true land plants — the first successful terrestrial plants to possess true roots, stem and leaves, and the only Cryptogams that possess vascular tissue. Their conducting system, however, is still primitive by the standards of seed plants.

Habitat. Pteridophytes generally grow in moist, shady places (e.g. ferns, horsetail), though some are aquatic (Azolla, Marsilea), some xerophytic — adapted to dry conditions (Equisetum) — and some epiphytic (Lycopodium).

Leaves. Leaves may be small, called microphylls (e.g. Selaginella), or large, called macrophylls (e.g. Nephrolepis/ferns).

Life cycle. Pteridophytes show heteromorphic alternation of generations: the sporophyte is diploid, dominant, autotrophic and independent, and it is differentiated into root, stem and leaves. Its primary root is short-lived and is soon replaced by adventitious roots, while the stem may be aerial or underground. Leaves vary from scaly (Equisetum) to simple and sessile (Lycopodium) to large and pinnately compound (Nephrolepis/ferns).

Vascular tissue. In these plants, the xylem consists only of tracheids and the phloem consists only of sieve cells. Because Pteridophytes lack cambium, they show no secondary growth. …