Early prehistoric plants. Computer artwork of Cooksonia caledonica plants on a mound of ancient lava at sunset during the Late Silurian period (445-416 million years ago). The first land-based plants to emerge from the waters were simple plants, only a few inches tall, consisting of slender branching stalks with rounded structures called sporangia. The sporangia, common to fungi and non-seed plants today, produced and contained the spores required for reproduction. Cooksonia were an important component of the Earth's flora until the early Devonian period (about 416 million years ago).