Plant Evolution

After plants originated from an algal ancestor approximately 470 million years ago, early diversification gave rise to seedless, non-vascular plants, including mosses, liverworts, and hornworts. These plants are formally called bryophytes, resemble other plants in having apical meristems and embryos that are retained on the parent plant, but they lack true roots and leaves. Without lignified cell walls, bryophytes with an upright growth habit lack support. The origin of vascular plants occurred about 425 million years ago. Their lignin-hardened vascular tissues provide strong support, enabling stems to stand upright and grow tall on land. Two clades of vascular plants are informally called seedless vascular plants: lycophytes and widespread monilophytes. The first vascular plants with seeds evolved about 360 million years ago. Seeds and pollen are key adaptions that improved the ability of plants to diversify in terrestrial habitats. A seed consists of an embryo packaged with a food supply within a protective covering. -Biology book pg. 344

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