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CPIE Notebook - Grasses of Hawai‘i and Guam Grass Key – Page 1
Key to Family Poaceae

The key to grasses extant in the Hawaiian Islands and Guam starts here, although if you are uncertain whether or not the plant you are trying to identify is a true grass or just looks something like a grass (may be a sedge, for example), you may want to start with couplet [94] on Monocots. Structural details pertinent to grasses are discussed and illustrated at various places in the key; however, some basic descriptive terms are defined on Page iv and these should be understood before starting the key. In this key, items in bold are intended to point out the most salient difference(s) in a couplet, but should not be considered alone until you become experienced with identifying grasses using the key. In other cases, a word in bold follows a non-technical term to familiarize these to the user. Note that any text following a curly brace "{" provides additional information that may be helpful but is not definitive of the species.

Figure 1A
Figure 1A. Grass vegetative anatomy: terms used to describe leaf and stem parts. (Left) A Digiteria with leaf pulled back to expose membranous ligule. (Right) Urochloa distachya with inflorescence branches just exserting from the leaf sheath; flower parts are contained in the spikelets and discussed in detail on page v.
leaf blade and sheath picture
[START OF GRASS KEY]

 . .
10a (To last page9) bamboo leaves Large or very large grasses with woody stems (called culms); side branches with leaf blades attached by pseudo-petioles. Basal leaf sheath papery with a small blade at top. Bamboos.
    ~ Subfamily BAMBUSOIDEAE
pseudo-petiole drawing 		[24]
10b

Plant size small, medium, large, or maybe very large, but culms never woody. Leaf typically consisting of a blade and a basal part (called a sheath; see Fig. 1A) clasping the stem, but open along a suture (unlike some sedges with closed sheaths, if present) and arising at a node on the culm .. .

[11]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
11a (10) Grass unusually robust, large or very large and plant rather coarse in comparison with typical grasses, either reed or cane-like: having a stiff, hollow and jointed stem (although, not hollow in sugar cane) and/or forming very large clumps with or without visible culms; OR if not exceptionally large, then densely clumping and leaves having a strong odor when crushed .. . [15]
11b

Plant otherwise: size may be delicate to large, but neither cane-like nor an especially large clump; leaves not having a strong odor upon crushing .. .

 [12]
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[NOTE THREE CHOICES HERE]
12a (11) Leaves linear, with most blades (or at least the lower ones) more than 10X longer than wide [20]
12b

Leaves longer than wide, but not linear, generally only about 6 times (or less) longer than wide (see Figures 1D and 1E, below)

 [13]
12c Leaves generally about 10 times longer than wide or a little more, 1 to 6 in (3 to 15 cm) long, much prolonged at the tip (acuminate). Spikelets compressed laterally; lemma bone white. { Small, creeping grass resembling Oplismenus (but leaves not wavy) with an inflorescence similar to a Panicum (no awns). [HAW - NAT]
    Cyrtococcum patens (L.) A. Camus
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
13a (12) Leaves heavy, narrow elliptic, 2 to 3 inches (up to 9 cm) wide and 5 or 6X longer than wide; parallel veins forming prominent ridges on upper leaf surface. { Clump-forming, medium size grass found in lowland, mesic or wet forests and along streams (Fig. 1D). Palmgrass (for its resemblance to palm seedlings) [HAW - NAT] [FAC]
    Setaria palmifolia (J. König) Stapf
palmgrass
Figure 1D. Palmgrass (Setaria palmifolia) in flower.
13b

leaves of basketgrass Leaves 1 to nearly 6 in (2-15 cm) long, usually 1/2 in (1 cm) to 1 in (2.5 cm) across, surface smooth but wavy (Fig. 1E). { Sprawling grasses common to abundant in shaded locations.

Figure 1E (left). Leaves of basketgrass, Oplismenus hirtellus

Figure 1F (below). Flowering head of O. hirtellus with awned spikelets arranged on racemes.

Flower head of basketgrass

[14]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
14a (13) Spikelets (compact cluster of flowers on a lateral stem, see Page 4) on lowest raceme no more than 3/16 in (4 mm) apart. Leaves to nearly 4 in (5-10 cm) long, usually about 1/2 in (1 cm) but less than 3/4 in (2 cm) across. { Small, sprawling grasses common to abundant on forest floors in lowland mesic forests. Basketgrass or hohono kukui. (Figs. 1E, 1F) [HAW -NAT] [FAC] [GUM - IND]
    Oplismenus hirtellus (L.) P. Beauv.
14b Spikelets on lowest raceme from 3/16 to 1/2 in (4 to 12 mm) apart. Leaves 1 to 6 in (2-15 cm) long, about 1/2 in (1 cm) to 1 in (2.5 cm) across. { Small, sprawling grasses common on forest floors in mesic forests above 800 ft (245 m) elevation. [HAW -NAT] [FACU] [GUM - IND] [FACU]
    Oplismenus compositus (L.) P. Beauv.

Synonyms for grasses on this page:

    Oplismenus undulatifolius (Ard.) Beauv. (= Oplismenus hirtellus)
ToC ToC  Basic Grass Description GRASS BASICS  Grass Key Introduction HAWAI‘I INTRO  Grass Key Introduction GUAM INTRO  Key to Lawn Grasses LAWN GRASSES  AECOS AECOS, Inc.

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