Common Grasses Introduction

About this Guide

This guide is designed to be helpful to both professional and amateur botanists. It covers the most common species, defined for the purposes of this guide as those that appear in at least half of the counties of Minnesota, regardless of whether they are native or not. A few species do not meet this criterion but are included because they are extremely abundant in the Twin Cities area. The descriptions provided are not intended to be complete and technical terminology is limited as much as possible. Those interested in agrostology (the science dealing with grasses) or in gardening with grasses will benefit from the references at the end.

The guide is arranged according to the scientific name but before the reader moans let us consider the issue of name standardization. While scientific names may seem foreign and difficult, they are, nevertheless, the most reliable and are applicable regardless of the native language. I believe most serious gardeners will not find this a daunting issue, since scientific names are becoming more and more "common" in the nursery trade. Those already familiar with scientific names will tell you that the names can tell you many things about the species in question. For instance, all species of Lilium will have three sepals and three petals that look alike; in the center will be six stamens and a three-carpellary gynoecium. Furthermore, the words that make up scientific names also have specific meanings. Albiflora, for example, means white (albi-) flowers (-flora); canadensis means first found (-ensis) in Canada (canad-); capillare means fine strands (as in capillary blood vessels).

Common names have no recognized standard, even within the state, and at times they can be confusing. For example, Indian grass is definitely a grass but blue-eyed-grass is a relative of irises, a completely different plant group. Changing from region to region or among cultures, the same common name can be applied to different species or different common names to the same species, without any guidelines. Common names may or may not have meaning. There are several plants, for instance, called blue bells Campanula, Mertensia, and Phacelia, because the flowers are variously bell-shaped and blue but they have very little else in common. Now in all honesty, the scientific name sometimes changes as well but there are very rigid rules that guide such changes. All changes must also be published with the reasoning for the change. The scientific names used in this book are based on the classification presented in Gleason & Cronquist, 1991, "Manual of the Flora of the Northeastern United States and adjacent Canada". The Flora of North America Project (FNA) will soon publish a new classification of the grass family, but in the interests of simplicity and not wanting to confuse the matter further, name changes occurring in FNA are not yet followed here.

All photographs the author's unless otherwise noted. No images may be copied without written permission.

Introduction to Grasses

The grass family (Poaceae) is one of the larger flowering plant groups, containing approximately 500 genera and 8000-9000 species. The largest genera in the family are Poa, the bluegrasses, with about 300 species; Eragrostis, love grass, with 300 species, Stipa, the needle grasses, approximately 250, and Paspalum, beadgrass, with 200. Grasses are distributed worldwide on all seven continents (one species of Trisetum is native to Antarctica) in a variety of habitats, from the frigid arctic and alpine tundras to tropical rainforests to scorching deserts. The majority of species, however, are found in the various grasslands, prairies, steppes, and savannas. Most are herbaceous with only the bamboos woody. Mature size ranges from less than 1 dm (4 in) to 40 m (144 ft), in the bamboo Dendrocalamus.

True grasses can sometimes be difficult to distinguish from one another and, to add to the confusion, there are a few other plants that superficially resemble grasses. The blue-eyed-grass mentioned above has long, narrow, grass-like looking leaves but the flowers are conspicuous with bright blue, white, or yellow perianths. The sedges, Carex, have grass-like leaves but the leaves all originate from the base of the plant and the flowers aren’t at all like grass flowers (yes grasses have flowers; more on that below). The rushes (Juncus) are also grass-like but the small flowers have papery tan sepals and petals, in many ways similar to the lily family.

Unlike most other plants, grasses have meristematic tissue, in the nodal areas (where leaves are attached to the stems) and at the base of the leaf blades, that can easily regenerate new leaves and stem tissue. Repeated pruning by either grazing animals or mower blades enhances vigor and growth continues. Most other plants will cease growth if they are constantly pruned back to the stem or have leaves eaten off. Grass growth, in general, occurs according to two seasons. Cool-season grasses produce most of their growth during the fall to spring period and slow their growth or even become dormant during the summer. Flowering takes place in spring. Such grasses generally require more moisture than the next category. Typical cool-season grasses include Kentucky bluegrass (Poa pratensis), the fescues (Festuca spp), wild-ryes (Elymus spp.). Warm-season grasses are just the opposite, dormant during the winter and then beginning their growth in the spring and early summer. These grasses are drought tolerant and generally bloom in late summer or fall. Examples include crabgrass (Digitaria spp.), bluestem (Andropogon spp.), and Indian grass (Sorghastrum nutans).

The Grass Plant

Parts of GrassLeaves are generally attached to the stem in two ranks, or sometimes spirally arranged, but never three ranked. Grass leaves consist of two parts, a "blade’, which may be very flat and broad or rolled and narrow, and a basal "sheath", which surrounds the stem and often is at least as long as the blade. The area where the blade and sheath merge is called the "collar" and usually there is a membranous flap or a ring of hairs at the collar, called the "ligule".

Since grasses are classed as angiosperms (flowering plants), they do have flowers. Though not very showy the grass flower is very simple, consisting of two united carpels (the female reproductive organs) surrounded by three stamens (the male reproductive organs); bamboos and wild rice are the exceptions with three carpels and six to numerous stamens. This is the essence of the grass flower; there are no petals or sepals. Two additional tiny membranous scales or "lodicules" can sometimes also be found associated with the reproductive organs. These are thought by many botanists to represent vestigial perianth parts. They play a role in opening or spreading floral parts at maturity, to aid in the free flow of pollen.

Grasses Plant Guide

The flower is then surrounded by two bracts, an inner "palea" and an outer "lemma". This whole structure, the flower and these two bracts, is called a "floret". One or more florets are then clustered together with two additional bracts at the base, called "glumes" (sometimes only one glume is present and very rarely both are lacking). The glumes may or may not resemble the lemmas. The lemmas or glumes may have an "awn" or long needle-thin appendage usually attached at the tip or sometimes to the back. The cluster of florets and glumes is called the "spikelet". Spikelets are then arranged in various inflorescenses: spikes (individual spikelets are attached directly to the main flowering stalk), racemes (each spikelet sits on a separate little stalk attached to the main flowering stalk), panicles (basically branching racemes), or combinations thereof. The panicle is the most common type of inflorescence in our species.

Floral diversity is directly related to pollination. Grasses, however, lack the showy perianth that attracts, traps, or rewards insects in other plants. Grasses rely instead on a pollinating agent other than insects, namely wind (the tropical Pariana is one of the few insect pollinated grasses [Soderstrom, T.R. and C.E. Calderon, 1971, Insect pollination in tropical rain forest grasses. Biotropica 3: 1-16.]). Since wind is not at all predictable in terms of carrying pollen to a suitable mate, grasses must produce copious amounts of pollen to increase the chances of a successful mating. As stamens mature and are ready to shed their pollen, the stalk or filament becomes flaccid allowing the stamen to dangle freely outside the floral bracts, where wind currents can easily carry the pollen away. Carpels of the same flower generally mature later so that most pollen from one flower will only be effective on the carpels of other flowers (this is not a hard-and-fast rule however). As carpels mature, the floral bracts again open wide exposing the feathery stigmas to the pollen-laden breezes. Once pollination occurs, the lemma and palea close and the two carpels together mature into a single one-seeded fruit, the "caryopsis" or "grain". Although each fruit produces only one seed, the many-flowered inflorescences provide an ample supply of seeds to renew and perpetuate the population.

Grasses and Grasslands

Grass communities also form important ecosystems--the prairies and savannas of mid-continental regions. Grasslands produce a vast amount of biomass, especially in their root system, that eventually breaks down and provides the rich source of nutrients that lures farmers. It is no coincidence that the best farming regions in the world occur in the major grasslands.

In the United States, the prairies of the Great Plains once covered the continental midsection, from central Indiana to central Montana and from central Canada to Texas. In Minnesota, it is estimated that the tall-grass prairie once covered about one-third of the state, from the western counties to the Twin Cities, and across the south into Wisconsin. When European settlers came into this region, the seemingly endless prairie was looked upon as a source of new wealth, new lives, and new dreams. But the settlers’ concern for survival overshadowed their understanding of how the prairies worked. Acre after acre was transformed into the Nation’s breadbasket.

It wasn’t until World War II that the few voices promoting conservation of all resources began to be heard and acted upon. Various governmental agencies and private organizations, such as The Nature Conservancy, began preserving whatever prairie remnants could be found. Concerned landowners began to realize they too could help preserve and conserve our prairie heritage.

Today more efforts are being directed to obtain additional property or to introduce management to connect the various sites already preserved. These prairie corridors and larger preserves re-establish some of the ecological workings of prairies as well. Towards this end, prairies are also being re-established on abandoned farmlands, matured parks, and overgrown savannas. Most successful farmers will tell you that planting all your hopes on one crop is foolhardy. Disease, storms, and other unforseen natural events can devastate your crop. Successful farmers introduce field rotations as well as variability in crop choices, including growing native plants.

The original prairie was a vast biodiversity melting pot that developed over centuries. Re-establishing this complex mix is a daunting project that must consider soils, micro-climates, seed sources, plant-animal interactions, weed control, wildlife cover and food sources. While it would be impossible to re-establish original prairie throughout the Great Plains, a smaller scale is do-able. At least 200 to 1000 continuous acres are considered minimum to re-create botanical diversity and introduce bison interaction (J.R. Thompson, 1992, "Prairies, Forests, and Wetlands", Univ. of Iowa Press, Iowa City). Restoration can not stop with establishment, maintenance must be an on-going process, including the use of prescribed controlled burning.

Grass Economics

The family is extremely important economically, providing the majority of foodstuffs for humans and a variety of forage for livestock. It contains such staples as wheat (Triticum), rice (Oryza), corn (Zea), oats (Avena), rye (Secale), sorghum (Sorghum), barley (Hordeum), and sugar cane (Saccharum). Some of the forage and turf grasses include bead grass (Paspalum), bluegrass (Poa), bluestem (Andropogon, Dichanthium), fescue (Festuca), gramma grass (Bouteloua), timothy (Phleum), wheatgrass (Agropyron, Elytrigia, Elymus), and zoysia (Zoysia).

The increasing interest in gardening with grasses has also introduced several others into our vocabulary: little bluestem (Schizachyrium), Indian grass (Sorghastrum), fountain grass (Pennisetum), hair grass (Deschampsia), and others. Several of the genera are considered to be fine accent plants and others (especially the warm-season grasses) are planted for their winter color. Genera such as Miscanthus, Festuca, Andropogon, and Panicum virgatum are widely planted in northern gardens.

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Copyright 2002, A.F. Cholewa, J.F. Bell Museum of Natural History, University of Minnesota / No portion of this guide may be duplicated without written permission of author.