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

Using a Dichotomous Key

If you are new to using or understanding a dichotomous key, the Introduction (and links provided) to Keys to the Aquatic Biota of the Hawaiian Islands will be useful. In particular, you should read the "Beginner's Orientation" section describing how our keys are set-up and how they are used.

Specialized Terminology

Grasses and sedges present an additional challenge independent of your experience or familiarity in using a dichotomous key: botanists have developed a fairly specialized terminology for the structures of a grass and especially the grass flower (forget "petals" and "sepals"). The terminology appplied to sedges is similar. You will need to gain an understanding of this terminology and A Key to the Common Grasses and Sedges of the Hawaiian Islands is set up to make this (hopefully) as painless as possible.

Information Sources/Corrections

This key is based upon the knowledge and personal experiences of the author, but also relies heavily on the references cited on Page vi. All photographs and drawings are those of the author, unless credited otherwise. We very much welcome comments on the key, and particularly concerning any couplet that is confusing or leads in a erroneous direction. Send comments to the author (


The organization of a dichotomous key can be either diagnostic (natural) or synoptical, the latter reflecting scientific classification based on evolutionary relationships, the former more appropriate to a key intended for less rigorous field or "home" use and limited in scope (as here, to commonly occuring grasses and sedges within a limited area). A standard organizational technique in a diagnostic key is to sort out the most obvious structural differences early in the key and then progress through ever finer details. This approach has been used on Page 1 in sorting out woody bamboos (clearly distinct from other grasses) from all other grasses at couplet [10] and then grasses with other than clearly linear leaves at couplet [11].

As indicated in the Introduction, a secondary goal of this guide is to move the user to an identification without requiring the close examination (using a magnifying lens) of miniscule grass structures like glumes and ligules. A "secondary" goal because for many species of grass, confirmation of an identification is usually not possible without resorting to this level of "detail". Yet many of our common grasses can be recognized on sight. To this end, lists of the most common grasses in the Islands are given at appropriate places in the key. These short lists allow the user to "jump" to a likely conclusion, where a description and photograph(s) might provide sufficient confirmation of a correct identification.


Using the "listing of most common grasses" described in the previous paragraph is a short-cut of sorts for those not really into keying things out, but just hoping to ID a common grass plant. For those with a good deal of knowledge about grasses, jumping ahead in a key to the details is also a short-cut. To facilitate this, the Table of Contents following may prove useful; but be cautious, as skipping early steps in a key can easily mislead. Confirmation of a correct identification may require far more information than is provided in a terminal couplet.

The Grasses
     Basic characteristics of grasses
     Basic characteristics of grass flowers
     Start of Grass Key [couplet 10]
Page iii
Page iv
Page v
Page 1
The Sedges
     Basic characteristics of sedges
     Basic characteristics of sedge flowers
     Start of Sedge Key [couplet 10]
Page vi
Page vi
Page vii
Page 30
Rushes Page vii
Very Large Grasses Page 2
Bamboos Page 3
Grass Inflorescence Types Page 4
Two or More Racemes or Spikes
    Genus Paspalum
    Genus Digitaria
Page 5
Page 6
Page 7
"Foxtail" Inflorescences
    Genus Cenchrus
Page 8
Page 9
Spike and Spike-like Inflorescences
    Genus Sporobolus
Page 10
Page 11
Digitate Inflorescences
    Genus Chloris
Page 12
Page 13
Paniculate Inflorescences
    Genus Dichanthium
    Genus Eragrostis
Page 14
Page 18
Page 19
Lawn Grasses Page 20
Bibliography Page x
Index (List of Species) Page xi

© 2012-16 AECOS, Inc. [FILE: Grass_Intro_ii.html] Introduction / ToC
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