Grass: Green, Grain, Grow

Grass in a Plant Round-up

THE FAMILY TREE OF GRAMINEAE

William A. Dayton

THE WORD grass supposedly evolved from an old Aryan root, ghra-, to grow. It is related to grain, green, grow, and the Latin gramen, grass.

The Oxford Dictionary gives the primary definition of grass as "herbage in general, the blades or leaves and stalks of which are eaten by horses, cattle, sheep, etc." This elemental usage is reflected, for example, in the Bible ( . . . all flesh is as grass, and all the glory of man as the flower of grass). Now, however, grass primarily refers to the natural botanical family of grasses (Gramineae or Poaceae).

Grasses belong to the seedplant subkingdom (Spermatophyta) and thereunder (1) to the subdivision of angiosperms (Anglospermae) with rudimentary seeds (ovules) enclosed in an ovary, and (2) to the class monocotyledons (Monocotyledones), the embryos of which have one seedleaf, or cotyledon.

Grasses are herbaceous and, sometimes, woody plants. Their stems, or culms, are jointed and the joints (nodes) are closed and solid; otherwise the stems mostly are hollow, although the number of solid-stemmed grasses, especially in the more and sites, is considerable.

The leaves, alternate in two ranks, are parallel-veined, consisting of a basal portion (sheath) enveloping the stem, ligule (marked G in the drawing), and blade. Ligule is derived from the Latin word ligula (literally, "little tongue"), a narrow strap as in a shoe latchet. The ligule, a characteristic feature of the grass family, is quite constant in a given species and is often an important means of distinguishing grasses, especially when not in flower or fruit. It is a projecting, often tongue-like, membranous end of the lining of the leaf-sheath, seen at the base of the leaf-blade, between it and the stalk; sometimes it is reduced to a mere fringe of hairs or to a hardened ring.

The flowers of grasses are mostly perfect (i. e., with both male and female floral organs), although occasionally they are one-sexed, mostly rather small, arranged primarily in small clusters (spikelets) on a central axis (rachilla), and containing (besides the floral organs themselves) two to many two ranked bracts (A). The two lowest and empty bracts are termed glumes, although occasionally one or both of these may be absent; above the glumes are one to many lemmas, or "flowering glumes" and opposite each of these is often a second, two-nerved bract called the palea (A, B).

The stamens, or male floral organs, are usually three but vary from one to six in number and have two-celled anthers. The pistil, or female floral organ, is solitary, with a one-celled ovary and usually two (rarely one or three) styles and stigmas; the latter are usually feathery (plumose). The perianth or corolla of more showy flowers is often represented in grasses by some rudimentary appendages known as lodicules, usually two (sometimes three) in number, which are small, thin, more or less translucent scales (B). These help to force open the lemma and palea, at the time of anthesis, to aid in fertilization.

The spikelets are usually themselves aggregated into terminal spikes, panicles, and racemes (D, E, F).

The fruit of grasses is a caryopsis, the seed and fruit being united, the seed adhering throughout to the thin outer fruit-covering, or pericarp (C). The caryopsis may be free, as in wheat and dropseeds (Sporobolus), or tightly invested, as in three-awns (Aristida) and gramas (Bouteloua).

Grasses form a large natural family comprising about 600 genera. Of these about 150 genera and 1,500 species occur in the United States.

Our species represent 14 tribes, which are differentiated primarily on spikelet characters.

Use has been made in grass taxonomy by some modern investigators of the basic number, size, and changes in "arm"-length of the chromosomes. W. M. Myers, in The Botanical Review for June 1947, writes that, despite certain limitations, "chromosome numbers, size and morphology provide critical information regarding phytogenetic relationships when used in conjunction with morphological, geographical, and ecological studies."

Grasses, widely distributed and among the most numerous individually of all plants, often form savannas or pure grass types, of which the buffalograss-grama "shortgrass" areas known as the Great Plains of our Middle West are familiar examples. Grasses range in height from less than an inch to more than 100 feet. The greatest number of species is in the Tropics, but the greatest number of individuals is in cooler climates.

For those interested in studying grasses, an admirable introduction is Mrs. Agnes Chase's First Book of Grasses. Though long officially retired, Mrs. Chase works every day in her office in the Smithsonian Institution and maintains her world-wide interest in systematic agrostology.

THE AUTHOR--William A. Dayton is in charge of dendrology and range forage investigations of the United States Forest Service. He is probably best known for his publications on native range plants and is joint author, with Harlan P. Kelsey, of Standardized Plant Names. Mr. Dayton has been connected with the Forest Service since 1911, and has been chief of the dendrology and range forage investigations since 1942.