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Plants that produce grains, fruits and vegetables form humankind's basic foodstuffs, and have been domesticated for millennia. They are used as ornaments and, until recently and in great variety, they have served as the source of most medicines and drugs.
The scientific study of plants is known as botany, a branch of biology.
Green plants have cell walls containing cellulose and obtain most of their energy from sunlight via photosynthesis by primary chloroplasts, derived from endosymbiosis with cyanobacteria.
Their chloroplasts contain chlorophylls a and b, which gives them their green color.
These groups appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event.
This is the broadest modern definition of the term 'plant'. brown algae/diatoms, haptophytes, dinoflagellates, and euglenids) not only have different pigments but also have chloroplasts with three or four surrounding membranes.
There are about 300–315 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants (see the table below).
and are the basis of most of Earth's ecologies, especially on land.
This clade includes the organisms that eons ago acquired their chloroplasts directly by engulfing cyanobacteria (e.g., Plantae Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships.
The evolutionary history of plants is not yet completely settled, but one accepted relationship between the three groups described above is shown below.
This includes the flowering plants, conifers and other gymnosperms, ferns, clubmosses, hornworts, liverworts, mosses and the green algae, and excludes the red and brown algae.