Plant classification and unicellular algae

Arranging plants by similarity of features, origin and historical development is called plant systematics. The systematic units from small to large are: species, genus, family, class, division, plant world (modern systems also have “order” between family and class). A species is a group of plants whose organs are all alike, that live in one area and interbreed to produce offspring. Closely related species form a genus, and related genera form a family: the genera almond, apple, apricot, rose and hawthorn belong to the rose family. Monocots (lily, grass families…) and dicots (rose, nightshade, mallow families…) form two classes, which together make up the division of flowering (angiosperm) plants. The rule of naming a species with two words — genus first, then species — (binomial nomenclature) was introduced by the Swedish scientist Carl Linnaeus (1707–1778); scientific names are written in Latin: garlic — Allium sativum, onion — Allium cepa (Allium is the onion genus). For cotton: division — flowering plants, class — dicots, family — mallow family, genus — cotton (Gossypium), species — upland (“Mexican”) cotton (Gossypium hirsutum).