Morphology of Grasses in Illinois

Discover the anatomy of the grasses of Illinois and the characteristics the grasses share with other plants.

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    Learn more about the history of different types of grasses in Illinois and how the grasses have evolved over time.
    Photo by ErikaWittlieb
  • grasses
    “Grasses” by Robert H. Mohlenbrock, is an interesting read for anyone looking to learn more about the grasses of Illinois.
    Courtesy of Southern Illinois University Press

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  • grasses

Grasses: Bromus to Paspalum (Southern Illinois University Press, 2002) by Robert H. Mohlenbrock, is an insight into the variety of grasses growing in the Illinois area. Find out which grasses grow best and how they have evolved. If you live in the Illinois area, see if any of the grasses grow anywhere near you. This excerpt can be found in the “Introduction.”

Grasses belong to the family Poaceae (also  called  Gramineae). Until recently, most botanists grouped  grasses and sedges ( Cy­ peraceae) in the order Graminales (or Poales). Anatomical, morphological, and other more recent evidence show that, in addition to grasses and sedges, other families such as the Xyridaceae, Commelinaceae, Pontederiaceae, and Juncaceae share some of the same characters and  should be grouped together. This view is followed here so that these six families are considered to com- prise the Commelinales. The Xyridaceae, Commelinaceae, Ponte­ deriaceae, and Juncaceae are treated in Flowering Plants: Flowering Rush to Rushes ( 1970); the Cyperaceae will be forth­ coming in two subsequent volumes.

The nature of grass structures generally  is so different  from that of other flowering plants that a special terminology is applied to grasses. A thorough understanding of these terms will enable one to identitify more readily an unknown specimen.

Grasses are annuals, biennials, or perennials. Annuals have tufts of fibrous roots and live for a single growing season. Peren­nials may be tufted, or they may have rhizomes (horizon­tal, root-producing stems below ground, or they may have stolons (horizontal,  root-producing  stems  above ground, or a short, thick, subterranean crown.

The stem which bears the leaves and inflorescence is called the culm. While the culm may be hollow or solid, the nodes (where the leaves arise) are nearly always solid. The culms may be simple or branched. Often they are jointed (geniculate) near the base. Culms may be erect, divergent (spreading), or prostrate and matted.

Grass leaves are borne at the nodes in two planes along the culm. This condition is referred to as 2-ranked. Some­times, because of a twisting of the culm, the 2-ranked condition is not apparent. The leaf is composed of a blade and a sheath. The sheath wraps around and encloses a portion of the culm. If the margins of the sheath are united, forming a cylinder, the sheath is closed; if the margins are not united, the sheath is open. The blade is the free  portion of the leaf. It is parallel­ veined and generally elongated, although some grasses with rather short, broad  blades occur. The blades normally are flat, but they may be folded or inrolled into a slender tube (involute). Along the inner face of the leaf, where the blade adjoins the sheath, there is often a ciliate, membranous, or cartilaginous structure of varying size and shape known as a ligule. In some grasses, some of the leaves are not blade­ bearing, therefore consisting merely of sheaths.



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