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A CPIE Notebook Project – Grasses of Hawai‘i and Guam Grass Key – Page 9
Tribe Paniceae
Key to Genus Cenchrus Linneaus.
(9A) Fountain grass growing on lava

Grasses in the Genus Cenchrus are characterized by having an involucre (structures that surround as a group) of spines and/or bristles below and in some cases enclosing much of the spikelet; the whole (involucre and spikelet) falling as a unit from the rachis at maturity. The unit is referred to as a "bur", although not in all cases is the bur spiny or "sticky" on clothing or hair. The inflorescence is a highly modified panicle, the involucre thought to be modified branches. In simple practical terms, the flowering head resembles a single, terminal spike-like raceme.

Species formerly treated in the genus Pennisetum are now included in Cenchrus. The genus includes one native (endemic) species (C. agrimonioides) in Hawai‘i, a species listed as endangered (USFWS, 1995). Other members of the genus are widespread and common in Guam and Hawai‘i.
[GENUS CENCHRUS]

      
46a Kikuyu grass Magnifying LensInflorescence (upon very close examination) is a few-spikelet spike enclosed in the uppermost leaf sheath, so only filaments and/or stigmas are exposed (see also Figure 20C). { Grass forming dense growth from rhizomes and stolens in dry to mesic open areas (see Fig. 9F below). Popular lawn and pasture forage at higher elevations on Maui and Hawai‘i Islands, but occurring on all the main islands (Fig. 9B). USDA noxious weed. Kikuyu grass [HAW - NAT]
    Cenchrus clandestinus (Hochst. ex Choiv.) Morrone
46b

Inflorescence not mostly hidden within a leaf sheath, but of multiple spikelets carried above the leaves and terminal on the culm. Plants clumping .. .

[47]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
47a (46) Plant forming a large clump with pink to deep purple or reddish bronze leaves .. . [58]
47b

Color of leaves mostly or entirely green .. .

[48]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
48a (To last couplet45) & (47) Magnifying LensSpikelet bristles soft, antrorsely scabrous (having tiny spine-like projections that point upward); if burr-like and attaching readily to clothing, NOT sharp and poking into skin .. . [52]
48b

Spikelet bristles hard and sharp, retrorsely scabrous (having tiny spine-like projections that point downward), and forming a rings of spines surrounding spikelet. A bur sharp to the touch .. .

[49]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
49a (48) Magnifying LensSpines on burs in two groups, the inner ones flattened, the outer small and rounded (terete) .. . [50]
49b

Burs with spines in a single group or series .. .

[51]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
[NOTE: THREE CHOICES HERE]
50a (49) burs of common sandbur Bur 4-7 mm (<1/3 in) long; spines connate (melded together into a cup) surrounding spikelet upwards to at least half the length; bur more or less globose. { Small, bunching grass typically found in drier areas, often near the ocean shore (Fig. 9C). Common sandbur, ‘ume‘alu, mau‘u kukū [HAW - NAT] [GUM - NAT] [FACU]
       Cenchrus echinatus L.

Figure 9C. Inflorescence of Cenchrus echinatus with burs (spikelets) shedding from the zigzag rachis.
50b Similar to above (C. echinatus) but burs smaller, more delicate, and more crowded on longer and more numerous spike-like racemes. { Distribution similar to C. echinatus. Bur-grass [GUM - NAT]
       Cenchrus brownii R. &. S.
50c Bur 8-18 mm (0.3-0.7 in) long; spines connate (melded together in a flared ring) only around base of spikelet with numerous smaller bristles above and below; bur more spindle-shaped. { Medium bunching grass, very rare, occurring typically on sand and dry, rocky ridges. Kāmanomano [HAW - END]
    Cenchrus agrimonioides Trin.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
51a (49) Burs 5–7 mm long (< 1/3 in), scabrous, the spines grooved. [HAW - NAT]
       Cenchrus setigerus Vahl.
51b Burs >1 cm (3/8 in) long and conspicuously hairy; spines not grooved. [HAW - NAT]
       Cenchrus tribuloides L.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
52a (49)

Most bristles conspicuously ciliate.. .

[53]
52b Bristles glabrous, scabrous, or with very sparse hairs .. . [57]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
53a (52) spike-like panicle of buffelgrass Bristles detaching from the rachis with the spikelet at maturity, forming a soft bur that catches on clothing. Inner bristles ciliate (plume-like). { Color when fresh a shade of red or purple. Extremely common, medium-size, bunching grass in lowland dry areas in Hawai‘i (the dominant grass on leeward slopes)(Fig 9D). Buffelgrass [HAW - NAT]
       Cenchrus ciliaris L.

Figure 9D. Newly developing inflorescence of buffelgrass.
53b

Not forming a bur that catches on fabric. Bristles glabrous or antorsely scabrous or plumose (feather-like) .. .

[54]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
54a (53) Medium size grass forming dense bunches of tough, narrow appearing (because leaf blades are rolled around a thick midrib) leaves. Cylindrical, pink to purple panicles, 3 to 12 in (6 - 30 cm) long. { Forming distinct clumps on dry, open landscapes; especially prominent covering vast areas of lava flows in Kona (Island of Hawai‘i) (Fig. 9A). HDA Noxious weed. Fountain grass [HAW - NAT] [GUM - NAT]
    Cenchrus setaceus (Forssk.) Morrone
54b Small to large grasses with leaf blades not appearing wiry (up to 1.5 in or 4 cm across). Foxtail panicle may be purplish, but more typically yellow .. . [55]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
55a (54) culm of elephant gras showing hairs Perennial clumping grass. Culm below panicle with short to long hairs; rachis cylindrical or ribbed. Inflorescence up to 1 1/8 in (3 cm) in diameter. One bristle on each spikelet longer and stouter than all the others. Leaves glabrous or with long hairs at margins near blade base; ligule a thin membrane topped with tight packed hairs, to 3x length of membrane. { A large to very large, tufted grass found in wet areas, often close to streams; very common in upcountry Maui (Fig. 9E; see also couplet [58]). Elephant grass, Napier grass [HAW - NAT] [GUM - NAT]
       Cenchrus purpureus (Schumach.) Morrone
55b Culm below panicle with a few short or no hairs; rachis angular. Bristles generally straight; inner bristles of each spikelet all roughly the same size and plumose at base, without groove; densely ciliate, cilia generally obscuring spikelets. Spikelets 3.5 to 4 mm long. { Inflorescence up to 3/8 in (1 cm) in diameter. Typically medium or taller grass in dry, exposed areas; common on Guam. USDA noxious weed. Feathery pennisetum [HAW - NAT], Mission grass, sakate [GUM - IND/NAT]
    Cenchrus setosus Sw.
 On to
[56]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
56a (55) Inflorescence expanded and crowded with viviparus spikelets: plantlets developing on inflorescence (pseudo-vivipary) { Rare. For a recent article with photos, see S. Bhowmik & Datta (2014). [GUM - IND]
    Cenchrus setosus (as polystachios) f. viviparus Fosb. & Sachet
56b Inflorescence normal, about 3/8 in (1 cm) in diameter: spikelets not pseudo-viviparous. { Very common on Guam. [HAW - NAT] [GUM - NAT]
    Cenchrus setosus f. setosus Sw.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
57a (49)

Annual. Bristles under 1 cm (< 0.4 in) long, persisting. { Rare, from bird seed or use in hydromulch (waif population) (see also couplet [58]). [HAW-NAT]

    Cenchrus americanus (L.) Marrone
57b Perennial. Bristles greater than 1 cm (0.4) long, typically brownish purple in color, but deciduous after spikelets fall. Culm scabrous or minutely pubescent. [HAW-NAT]
    Cenchrus complanatus (Nees) Morrone
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
[NOTE: THREE CHOICES HERE]
58a (47)

Plant eventally growing to a cane up to 10 feet (3 m) in height. Inflorescence a purplish foxtail. Leaves greater than 20 cm (about 1 in wide). All bristles scabrous. { Burgundy fountain grass, burgundy giant [HAW - ORN]

    Cenchrus elegans (Hassk.) Veldk.
58b

Inflorescence a purplish foxtail. Leaves 10 cm or less in width. At least one inner bristle plumose { [HAW - ORN]

    Cenchrus xcupreus
58c

Inflorescence culms produced are sterile (fail to produce seeds). ( Large, clumping perennial resembling elephant grass with purple leaves; grown for forage. Bana grass [HAW ORN]

    Cenchrus americanus x purpureus

Species of Cenchrus (and Pennisetum) reported to be in Hawai‘i or Guam and either not
   covered in this key or included as a synonym under a more recent name (=new name):
    C. caliculatus Cav. [?HAW]
    C. caninus (Reinw. ex Blume) Marrone (= C. elegans)
    C. longisetus M.C. Johnst. [HAW ORN] (not naturalized in Hawai‘i [Faccenda, 2023a]).
    Pennisetum advena [in part] (= C. xcupreus)
    P. clandestinum Hochst. ex Chiov. (= C. clandestinus)
    P. complanatum (Nees) Hemsl. (= C. complanatus)
    P. glaucum (L.) R. Br. [HAW] [GUM] (= C. americanus)
    P. macrostachyum (Brongn.) Trin. (= C. elegans)
    P. orientale Rich. [GUM]
    P. polystachion (L.) Schult. (= C.setosus)
    P. purpureum Schumach.(= C. purpureus)
    P. setaceum (Forsk.) Choiv. (= C. setaceus)
    P. setosum (Swartz) Richard (= C. setosus)
    P. villosum R. Br. ex Fresen. (= C. longisetus)
  SUPPLEMENTAL PHOTOS
 [CLICK ON THUMBNAIL TO OPEN AN ENLARGED IMAGE]

Fig. 9F thumbnail
Figure 9F. Enlarge to see typical erect culm
and leaves of Kikuyu grass (Cenchrus clandestinus).
See also Figure 20C.
 
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