Poaceae or Gramineae is a family in the Class Liliopsida of the flowering plants. Plants of this family are usually called grasses. There are about 600 genera and between 9,000–10,000 species of grasses (Kew Index of World Grass Species). Plant communities dominated by Poaceae are called grasslands; it is estimated that grasslands comprise 20% of the vegetation cover of the earth. This family is the most important of all plant families to human economies: it includes the staple food grains grown around the world, lawn and forage grasses, and bamboo, widely used for construction throughout east Asia and sub-Saharan Africa.

The term "grass" is also applied to many grass-like plants not in the Poaceae, leading to plants of the Poaceae often being called "true grasses".

Structure and growth

Grasses generally have the following characteristics (it is advisable to have a look at the image gallery for reference):

General aspects

Grass blades grow at the base of the blade and not from growing tips. This location of the grass growing point near the ground allows it to be grazed or mowed regularly without damage to the growing point.

Reproduction

The fruit of Poaceae is a caryopsis.

Grass plants also spread out from a parent plant. Growth habit describes the type of shoot growth present in particular grass plants and is directly related to their ability to spread out from the parent plant and ultimately form a clonal colony. There are three general classifications of growth habit present in grasses; bunch-type, stoloniferous, and rhizomatous.

Cool and Warm Season Grasses

The success of the grasses lies in part in their morphology and growth processes, and in part in their physiological diversity. The grasses divide into two physiological groups, using the C3 and C4 photosynthetic pathways for carbon fixation. The C4 grasses have a photosynthetic pathway linked to specialized Kranz leaf anatomy that particularly adapts them to hot climates and an atmosphere low in carbon dioxide.

C3 grasses are refereed to as "cool season grasses" while C4 plants are considered "warm season grasses". Cool and warm season grasses can be annual or perennial.

• Annual Cool Season - wheat, rye, Annual Bluegrass, and oats
• Perennial Cool Season - orchardgrass, fescue, Kentucky Bluegrass and perennial ryegrass
• Annual Warm Season - corn, sudangrass, and pearlmillet
• Perennial Warm Season - big bluestem, indiangrass, bermudagrass, switchgrass, and old world bluestems.