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A CPIE Notebook Project – Grasses and Sedges of Hawai‘i Page iv

Basic Characteristics of Grasses

Structural details concerning grass identification will be introduced at various places throughout the key. To begin using the key, however, it is important to acquire an understanding of several very general terms used in describing grasses, such as growth form and size.

The size achieved by an individual grass plant can (like most plants) vary considerably depending upon conditions under which it grows, so realize that the size categories described here (small, medium, large, and very large) are not absolutes but intended as guides to help confirm an identification. As a rule, a particular grass species will not be larger than the size given, but may be smaller if growing under adverse conditions or regularly cropped by ungulates or lawn mowers. Once a grass is in flower, that plant is (within the broad categories used here) as large as it is going to get. The terms used in the key for grass plant size are defined as follows:

Small Grass plant under 12 inches (30 cm) in height, usually ankle or shin high; lawn grasses, love grasses, crab grasses.
Medium – Grass plant greater than 1 foot and up to 3 feet (0.3 to 1 m) tall: typically between knee high and waist high; pili, kāwelu.
Large Grass plant typically over 3 feet (1 m) in height up to about 10 feet (3 m); from stomach or chest high to over your head; Sugar cane, Guinea grass, Job's tears, California grass.
V. large Grass plant greater than 10 feet or 3 m; some bamboos can exceed 70 feet (20 m) in height.

Growth form and persistence (or duration) are important characteristic useful for describing a grass species. Grasses are usually distinguishable as one of two basic growth forms: running (spreading by rhizomes or stolons or both) or tufted (bunching or clumping).

Bunching grass Figure E. This photo (click on it to enlarge), taken in an Ulupalakua Ranch pasture at about the ~2000-ft (~600-m) elevation, shows a medium-size, perennial tufted grass (Cymbopogon refractus) with a small running grass (probably Kikuyu) covering ground between the tufts.

Another consideration related to growth form is whether a grass is an annual or a perennial. Although at first, this characteristic would seem impossible to apply in the field, various clues can be used to indicate duration. Running grasses are perennial, as, typically, are the larger tufted grasses. The latter may die back to crowded basal stems in the dry season, but the tufts put out new growth in subsequent years. Small, tufted grasses tend to be annuals, their dried remains not regenerating with the onset of the wet season and the population continuing only through germination of seeds dropped by the previous generation. Because of our mild climate, some annuals may persist beyond a year in favorable locations (for example, see Fig. F, below). In the photo above, both grasses would be judged to be perennial: the tufted species because of the density of leaves (both dried and fresh leaves are present after completion of this year's flowering); the spreading grass because annuals simply do not form extensive mats, the result of spreading by rhizomes or stolons.

Plant Status—By plant status is meant the origin of a species (or subspecies) relative to the Hawaiian archipelago. That is, plants are either native or not native (= alien, introduced) to Hawai‘i, and this information is provided in the key in brackets at the identification couplet. Coding in the key appears as follows:

    [END] – endemic; a plant that is native, evolved in the Islands; unique to Hawai‘i;
      not native to any other places in the world.

    [IND] – indigenous; a plant that is native, arriving in the Islands on its own, but also native to other places.

    [NAT] – naturalized; a plant alien to the Islands that has naturalized (adapted to the "wild"); NOT native.

    [ORN] – ornamental; a plant alien to the Islands that is not naturalized; used in landscaping or agriculture.

    [POL] – Polynesian introduction; a plant brought to Hawai‘i by the early Polynesian settlers (a "canoe" plant).

Of the at least 150 grass species found in the Hawaiian Islands, 8 species are indigenous and 39 are endemic (Wagner, Herbst, & Sohmer, 1990). Two species are presumed Polynesian introductions: or sugar cane (Sacharum sp.) and ‘ohe ("native" bamboo, Schizostachyum glaucifolium). Unfortunately, the endemics are difficult to locate as they are absent or rare in the lowlands around the islands. Several indigenous species are easy to find, if you know where to look. For example, ‘aki‘aki (seashore rushgrass, Sporobolis virginicus) can be found in dunes and soil behind the active beach all along our shores.

Bambusa sheaths Return to Introduction INTRODUCTION

Grass Inflorescence Basics GRASS FLOWER BASICS

Key to Grasses GRASS KEY

Fig. F. Clumping grass, Sixweek threeawn (Aristida adscensionis), in North Kona on Hawai‘i Island. Although considered an annual, the two distinct colors of dried leaves suggest this species may be biennial here (6.0 MB).

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