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About 425 million years ago a new type of plant appeared: these were the vascular plants, with their lifestyle. The earliest known vascular plants come from the Silurian period.
The Pleistocene Ice Ages were significant in the evolution of New Zealand plants as, together with the new habitats formed by the rise of the Southern Alps, they provided the conditions for the development of our extensive endemic alpine flora.
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Two major groups of angiosperms are the dicotyledons (more correctly, "eudicotyledons") and the monocotyledons, which include the grasses. Grasses evolved in the Eocene (56.5 - 35.4 million years ago), and this led in turn to the evolution of browsing mammals during the Oligocene (35.4 - 23.2 million years ago). As the world began to cool during the Miocene (23.2 - 5.2 million years ago) these grasslands spread and the forests contracted; by the Pliocene (5.2 - 1.6 million years ago) there were deserts in many regions. The fragmentation of forest habitats, and spread of grasslands, that accompanied this cooling trend are implicated in the evolution of humans.
The owe their success to the evolution of the flower. The flower's pollen and nectar encourage pollinating animals to visit, increasing the odds of fertilisation by ensuring that pollen is transferred efficiently from flower to flower. (The flowers of wind-pollinated angiosperms, e.g. grasses, are very much reduced in terms of size and complexity.) After fertilisation the carpel and other parts of the flower are used to form fruit that aid dispersal of the seeds inside the fruit. In addition, the xylem of angiosperms allow very rapid movement of water through the plant. This means that flowering plants can keep their stomata open through much of the day, achieving higher photosynthetic rates than gymnosperms; this "spare" photosynthetic capacity can support the development of fruit.
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In comparison, a seed contains a young plant and a nutrient store for that plant. This means that seed plants (gymnosperms and angiosperms) can colonise areas with transient or sub-surface water as the young plant can establish itself extremely rapidly once it has germinated. The evolution of the seed underpins the success of the gymnosperms and angiosperms.
While spores are easy to disperse, they have few reserves to establish themselves. This means that a spore reach a wet area, germinate rapidly, and begin photosynthesising straight away to gain energy for the next phase of the lifecycle. Thus spore-producing plants are limited to wet environments for at least part of their lifecycle.
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means that the organism relies directly on the environment for its water. As a result, the organism's water content tends to reach equilibrium with that of the environment. Poikilohydric organisms have no mechanisms to prevent desiccation: they desiccate, and remain dormant, when their environment dries out, but can rehydrate when water becomes available again. They usually absorb water directly through their body surface.
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Once these features had evolved, there was a substantial diversification of land plants during the Devonian period (408 - 362 million years ago). These included lycophytes (the clubmosses are the best-known modern members of this group:), horsetails (e.g. Equisetum), and progymnosperms, intermediate between seedless vascular plants and the seed plants. While the early forms were small & lacked woody tissue, the first tree-like plants (including progymnosperms and tree-sized lycophytes) had appeared by the mid-Devonian. The first real trees (e.g. Archaeopteris) had developed by the late Devonian, and the seed-bearing had evolved from the progymnosperms by the end of this geological period. The appearance of trees had a significant effect on the environment, because their advanced root systems influenced soil production and led to increased weathering.
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These first land plants evolved from the green algae, with which they share a number of traits. All store energy reserves, as starch, inside plastids. Their cell wall is built of cellulose microfibrils and the photosynthetic pigments are chlorophylls a and b, plus b-carotene.
For Microfossils, stromatolites, and cyanobactieria:
Baragwanathia is much larger & more complex, with what appear to be spirally-arranged leaves. Baragwanathia has been described as a (a vascular plant). For such a complex plant to be present in the Silurian then land plants must have emerged much earlier, perhaps in the Ordovician.
To find out more about living stromatolites see:
In the Carboniferous (362 - 290 million years ago) conditions were warm, with little seasonal change in tropical latitudes, and the land was warm & swampy. These conditions suited the widespread forests horsetails & tree ferns that, like most other Carboniferous plants, reproduced by spores. Spores require moist conditions for germination and rapid growth. However, many of these spore-bearers died out as the environment became more arid towards the end of the Palaeozoic. The first conifers began to appear towards the end of the Carboniferous.
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