Rice, wheat, bananas, orchids and palm trees all share a one-leaf beginning
Monocots sprout with a single embryonic leaf, and this one group of over 70,000 species supplies most of the plant mass farmers grow. Grasses alone cover more than 40 percent of Earth's land. Yet monocots cannot thicken their trunks the way oaks do, which forced palms and bamboos into clever workarounds.
Monocotyledons, or monocots, are flowering plants whose seeds hold just one cotyledon. They were long contrasted with dicots, which have two, but two seed leaves turn out to be the ancestral condition of all flowering plants, so dicots do not form a natural group. Botanists now split them into eudicots and several older lineages from which both eudicots and monocots arose. The APG IV system accepts monocots as a genuine lineage without assigning a formal rank.
The single cotyledon is a poor field guide, since it lasts only briefly and is not entirely reliable. It is one of several changes in the ancestral monocot body plan, possibly linked to an early life in water before the move onto land. Even so, monocots are distinctive enough that botanists rarely argue over which plants belong.
Their defining limitation is the lack of a cambium, the layer that lets trees widen as they grow taller. That makes water transport and branching harder, and large monocots solve it in different ways. Some yuccas develop an unusual form of secondary growth, and palms thicken their base early in a process called establishment growth, producing an inverted cone at the foot of the trunk. Climbing aroids find host trees by growing toward darkness, and the rattan palm Calamus manan produces the longest shoots of any plant, up to 185 metres.
The economic stakes are huge. Maize, rice, wheat, barley, oats, sorghum and millet are all grasses, and dates, onions, garlic, sugarcane, bananas and ginger are monocots too. The group also includes orchids, tulips, lilies and daffodils, bamboo and reeds, bromeliads that perch on trees, and seagrasses living fully underwater.
Source: Monocotyledon
