| Dominant groups | Gymnosperms (conifers, cycads) • Angiosperms (flowering plants) |
| First emergence | Ordovician period, ~450 million years ago |
| Key adaptations | Vascular systems • Floral structures |
| Ecological impact | Shaped global climate • Drove development of terrestrial ecosystems |
| Symbiotic relationships | Fungi • Bacteria |
Plants are complex, multicellular eukaryotes that make up a major component of Earth's ecosystems. They first emerged as simple algae in the Proterozoic era over 1 billion years ago, but it was the rise of terrestrial plants starting in the Ordovician Period around 450 million years ago (mya) that had the most dramatic impact on the planet.
The earliest known terrestrial plants were primitive, non-vascular bryophytes like liverworts and hornworts. These simple mosses and lichens colonized the land in the Ordovician, evolving specialized sporophytes and gametophytes to reproduce. They preceded the rise of more complex vascular plants, which began diversifying in the Silurian Period around 420 mya.
The first true vascular plants were early ferns, horsetails, and lycopods, which developed primitive xylem and phloem to transport water and nutrients. These early tracheophytes grew up to several meters tall and reproduced via primitive seeds and spores. They soon became the dominant forms of vegetation on land.
A major evolutionary milestone was the emergence of the gymnosperms in the Carboniferous Period around 350 mya. These plants, which included conifers, cycads, and ginkgos, reproduced via exposed "naked" seeds rather than flowering. Gymnosperms proved extremely successful and diverse, dominating terrestrial ecosystems for hundreds of millions of years.
Conifers like pines, firs, and redwoods became particularly widespread, forming the iconic boreal and temperate forests across the Northern Hemisphere. Cycads, resembling palm trees, thrived in warmer climates. The lone surviving ginkgo species is considered a "living fossil" dating back to the Permian Period.
While angiosperms, or flowering plants, first emerged in the Triassic Period around 200 mya, they remained a relatively minor component of global plant life compared to gymnosperms for a very long time. It was not until the Cretaceous Period, around 100 mya, that angiosperms began to rapidly diversify and displace many gymnosperm lineages.
Angiosperms developed many innovations including flowers, fruits, and a more advanced vascular system. This allowed them to outcompete gymnosperms in many ecological niches. However, gymnosperms like pines and cycads remained dominant in boreal, temperate and tropical regions. Angiosperms never fully supplanted them as the most numerous plants on Earth.
Over their long evolutionary history, plants developed a wide array of specialized adaptations to survive in diverse environments. A key innovation was the evolution of symbiotic relationships with fungi and bacteria.
Many plants form mycorrhizal associations with soil fungi, which expand the plant's ability to absorb water and nutrients. Others host nitrogen-fixing bacteria that provide essential nutrients. These mutually beneficial relationships have been crucial to the success of terrestrial plants.
Plants also diversified their reproductive strategies, from simple spores to more complex seeds and fruits. Some developed elaborate pollination mechanisms relying on insects, birds and even bats. This co-evolution with animals further drove plant diversification.
The rise of terrestrial plants had a profound impact on the global environment. As the first major producers of oxygen through photosynthesis, plants fundamentally shaped the atmosphere and climate over millions of years. Their growth and decomposition also contributed to the formation of fossil fuels like coal and petroleum.
The development of extensive plant biomass reshaped landscapes, enabling the diversification of animal life in terrestrial ecosystems. Plants became the foundation of food webs, providing food and shelter for a vast array of organisms. Their evolution into towering forests, lush grasslands, and flourishing wetlands transformed the face of the planet.
Today, plants remain essential to maintaining the Earth's habitability, regulating the climate, cycling nutrients, and providing essential resources for countless species. Understanding the long history and ecological importance of these complex, amazing organisms continues to be a crucial area of scientific research.
