Pteridophytes

Pteridophytes (horsetails and ferns) were the first land plants with vascular tissue: xylem to carry water and phloem to carry food. That let them grow larger on land. People use them as medicines, as soil-binders, and as ornamental plants (many ferns in pots).

Here the main plant you see is the sporophyte, with a true root, stem and leaves. Leaves may be small (microphylls, as in Selaginella) or large (macrophylls, as in ferns). Spore-making sacs (sporangia) sit on special leaves (sporophylls), which in some plants are packed into cones (strobili), as in Selaginella and Equisetum.

Spores are made by meiosis. A spore grows into a small, flat, free-living green plant called the prothallus: this is the gametophyte. It needs cool, damp, shady places, and water is still needed for the antherozoids to swim to the archegonium. The zygote then grows into a new sporophyte, the big fern.

Most pteridophytes make one kind of spore (homosporous). But Selaginella and Salvinia make two kinds (heterosporous): large megaspores (female) and small microspores (male). In them the female gametophyte stays on the parent plant and the young embryo forms there. This is a step towards the seed habit, which seed plants later perfected.

Four classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum, the horsetail), and Pteropsida (ferns such as Dryopteris, Pteris and Adiantum).