4-16 Poacaeae, grass family

Abstract

Worldwide, the grasses provide about 7500 species and dominate the world‘s vegetation. Grasslands yielded our earliest civilizations and crops such as sugar, rice, corn, wheat, barley and rye are significant agricultural commodities.

As a family, they are difficult to identify. The species are variable, hybrids are common and there are many of them. Most will need magnification, even 10X aids in viewing floral structure on which the following keys depend.

Our grasses are herbaceous and the jointed culms arise from fibrous roots. The long narrow leaves are alternate, sheathing the stems. The sheaths are open. A membrane, the ligule, usually occurs adaxially at the junction of the sheath and the leaf blade. Two auricles may project from the ligule at either side of the leaf and partly encircle the culm. Ligule also may be papery, membranous or ciliate, and may be entire or variously torn. Both the ligule and the auricle provide key characters in their presence, absence or form.

The inflorescence is a spicate, paniculate or racemose arrangement of spikelets. Each spikelet has a pair of glumes subtending one or more florets alternating along the rachilla. There is a pair of bracts subtending each floret, called the lemma (lowermost) and the palea (top or distal bract). These may differ in presence, texture, size and shape. The basal portion of the lemma may be enlarged to form a callus. Awns may be present on the glumes or the lemmas. Typically there is one ovary surrounded by three stamens.

Fruits are achenes or more commonly caryopses. In the vernacular grass fruits are called grains and cultivated food grasses are often referred to as cereal crops.

In Nova Scotia, the grasses exhibit the greatest diversity (more genera) although the sedges have more species.

Photographic use provided by Roger Lloyd, sean Blaney, Marian Munro, Alain Belliveau, Martin Thomas and David Mazerolle.