The amphibians of the plant kingdom, the liverworts and mosses, and the first plants with vascular tissue, the pteridophytes, with their spores, prothalli and the first step towards seeds.
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Created by StemPy LabBryophytes live on land but need water for sexual reproduction, so they are called the amphibians of the plant kingdom. Their main plant body is the haploid gametophyte, held by rhizoids, with no true roots, stems or leaves and no vascular tissue. The sporophyte grows on the gametophyte and depends on it. Liverworts such as Marchantia form flat thalli and gemmae; mosses grow from a protonema into leafy shoots.
Pteridophytes, such as ferns and horsetails, are the first land plants with vascular tissue. Their main plant body is the diploid sporophyte, with true roots, stems and leaves. Sporangia on sporophylls make spores by meiosis; in some, the sporophylls form cones called strobili. A spore grows into a small prothallus that bears antheridia and archegonia, and needs water for fertilisation. There are four classes.
Most pteridophytes are homosporous: they make one kind of spore. Selaginella and Salvinia are heterosporous: they make small microspores and large megaspores, which grow into male and female gametophytes. The female gametophyte stays on the parent sporophyte, and the zygote grows into an embryo inside it. This is a step towards the seed habit. Both bryophytes and pteridophytes have a haploid gametophyte and a diploid sporophyte.
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