For Aristotle, anything alive that was not an animal counted as a plant
The ancient Greek scheme was simple: living things with a sensitive soul were animals, and those with only a vegetative soul were plants. Under that view the plant kingdom swept in fungi and algae alike. Modern biology has trimmed it sharply, and today fungi are out entirely, along with some of the algae.
Aristotle's student Theophrastus carried plant classification further, and many centuries later Carl Linnaeus built the foundation of modern scientific naming while keeping the two-kingdom split, calling plants Vegetabilia. Now the most common definition treats plants as the green plants: green algae plus land plants, from mosses and ferns to conifers and flowering plants. A genome-based definition widens the circle to include red algae and glaucophytes.
Roughly 382,000 plant species are accepted, and the large majority produce seeds; about 85 to 90 percent are flowering plants. They span an astonishing range of size, from single-celled forms less than 3 micrometres across to the conifer Sequoia sempervirens, which can reach 120 metres. Most make sugar from carbon dioxide and water using sunlight and chlorophyll, and those sugars power most of Earth's ecosystems while green plants release a large share of the planet's oxygen. A few lineages have turned parasitic instead, taking their energy from other organisms.
Plants began in water. An algal scum coated land 1,200 million years ago, but true land plants, organised like mosses, only appeared around 450 million years ago in the Ordovician. They diversified from the late Silurian, and a fossil bed called the Rhynie chert preserves early Devonian plants in cellular detail, turned to stone in volcanic hot springs full of silica. When the Devonian closed, roots, leaves and woody trunks had all evolved.
Carboniferous swamps were ruled by clubmosses and horsetails the size of trees, alongside the first seed plants. After the Permo-Triassic extinction reshaped life, flowering plants emerged and then spread so quickly in the Cretaceous that Charles Darwin called their rise an abominable mystery. Meanwhile conifers came to dominate Jurassic landscapes. Humans have domesticated grains, fruit and vegetables for millennia, and plants also provide timber, writing materials and ornament.
Source: Plant
