Which phase is the plant you see?

• Pteridophytes include horsetails and ferns. They are used in medicine and as soil-binders, and many are grown as ornamentals.
• In evolution they are the first land plants with vascular tissues, xylem and phloem. They grow in cool, damp, shady places, though some do well in sandy soil.
• In bryophytes the gametophyte dominates; in pteridophytes the main plant is the sporophyte, with a true root, stem and leaves, each with well-developed vascular tissue.
• Selaginella has small leaves (microphylls); ferns have large ones (macrophylls).
• Sporangia sit on leaf-like sporophylls. In some plants the sporophylls are packed into compact strobili or cones, as in Selaginella and Equisetum. Spore mother cells in the sporangia divide by meiosis to make spores.
• A spore grows into a small, inconspicuous but multicellular, free-living and mostly photosynthetic thalloid gametophyte, the prothallus. It needs cool, damp, shady conditions.
• The prothallus bears antheridia and archegonia. Water carries the antherozoids from the antheridia to the mouth of the archegonium, where one fuses with the egg to give a zygote that grows into the dominant sporophyte.
• Because the gametophyte needs such particular conditions, and fertilisation needs water, living pteridophytes are confined to narrow geographical areas.
• The group has four classes. Psilopsida: Psilotum. Lycopsida: Selaginella and Lycopodium. Sphenopsida: Equisetum. Pteropsida: Dryopteris, Pteris and Adiantum.

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