AgricultureID

Poaceae — the grass family

The grass family. It supplies more human food energy than any other plant family, and it does so through crops as unlike each other as rice, sugarcane and perennial ryegrass — so the family explains structure and physiology rather than agronomy.

A botanical family. Membership is a fact about the plants and is derived from the verified identities, never listed by hand.

The growing point stays low

Grasses grow from intercalary meristems at the base of the leaf and at the nodes rather than from an apex held aloft. That is why grasses tolerate being grazed and mown when other plants do not, and it is the single structural fact that makes pasture, lawn and cereal straw all possible from one family.

Tillering

A grass plant is a colony of tillers, each capable of producing its own roots and its own head. Plant population is therefore only loosely under the grower’s control: a thin stand compensates by tillering and a thick one self-thins, which is why grass crops are far more forgiving of establishment error than a crop that sets its final plant number at sowing.

Wind pollination and its consequences

Most grasses are wind-pollinated, and many are strongly outcrossing. That makes isolation distance a real constraint in seed production, makes hybrid breeding attractive where sterility systems exist, and is why cross-pollination between a crop and a weedy relative is a live concern in this family more than in most.

Both photosynthetic pathways

Poaceae contains both C3 and C4 crops, which is unusual for a single family and is why its members span such different climates. The C4 members — maize, sorghum, the millets, sugarcane — carry higher water-use efficiency and a higher temperature optimum, and the division cuts across the agricultural groupings rather than following them.

The family’s shared pathogens

Rusts, smuts, ergot and the blotch diseases are grass pathogens rather than crop pathogens, and several move between cultivated and wild grasses. That is why a grass weed in or beside a cereal crop is a disease question as well as a competition question, and why rotation out of the family is a disease-management tool in its own right.

What this is not

  • Cyperaceae — the sedges — look like grasses and are not; the corpus holds no sedge crops but the confusion matters for weed identification.
  • The cereals group is a subset of this family defined by end use, and excludes the sugar and forage members.