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A CPIE Notebook Project – Grasses and Sedges of Hawai‘i Page 9


Key to Genus Cenchrus L.
(9A) Fountain grass groeing 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).


[KEY TO 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. Kikuyu grass. (Fig. 9B) [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

[47]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
47a (46) Plant forming a large clump with deep purple to reddish bronze leaves; plant eventally growing to a cane up to 10 feet in height. Inflorescence a purplish foxtail. { Burgandy fountain grass. [ORN]
    Cenchrus caninus (Reinw. ex Blume) Marrone
47b Not as above. Color is green

[48]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
48a (45) & (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 [50]
48b

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

[49]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
49a (48) burs of common sandbur 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. Common sandbur, ‘ume‘alu, mau‘u kukū. (Fig. 9C) [NAT]
    Cenchrus echinatus L.


Figure 9C. Inflorescence of Cenchrus echinatus with burs (spikelets) shedding from the zigzag rachis.
49b

Spines connate (melded together in a 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. [END]

    Cenchrus agrimonioides Trin.
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
50a (48) 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 (the dominant grass on most dry, leeward slopes). Buffelgrass. (Fig 9D) [NAT]
    Cenchrus ciliaris L.


Figure 9D. Newly developing inflorescence of buffelgrass.
50b

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

[51]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
51a (50) 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). Fountain grass. (Fig. 9A) [NAT]
    Cenchrus setaceus (Forssk.) Morrone
51b

Small to large grasses with leaf blades not appearing wiry (up to 1.5 in or 4 cm across). Spike-like panicle may be purplish, but more typically yellow

[52]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
52a (51) culm of elephant gras showing hairs Culm below panicle with short to long hairs; rachis cylindrical or ribbed. Inflorescence up to 3/4 in (2 cm) in diameter. 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. Elephant grass, Napier grass. (Fig. 9E) [NAT]
    Cenchrus purpureus (Schumach.) Morrone
52b

Culm below panicle with a few short or no hairs; rachis angular. { Inflorescence up to 3/8 in (1 cm) in diameter. Typically medium or taller grass in dry, exposed areas. Feathery pennisetum. [NAT]

    Cenchrus polystachios (L.) Morrone


Species of Cenchrus (and Pennisetum) reported to be in Hawai‘i and either not
    covered in this key or included under a more recent name (=new name):

    C. caliculatus Cav.
    C. longisetus M.C. Johnst.
    C. setigerus Vahl.
    C. tribuloides L.
    Pennisetum clandestinum Hochst. ex Chiov. (= C. clandestinus)
    P. complanatum (Nees) Hemsl.
    P. glaucum (L.) R. Br.
    P. macrostachyum (Brongn.) Trin. (= C. caninus)
    P. polystachion (L.) Schult. (= C. polystachios)
    P. purpureum Schumach.(= C. purpureus)
    P. setaceum (Forsk.) Choiv. (= C. setaceus)
    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 branch of Kikuyu grass (Cenchrus clandestinus).

© 2014-17 AECOS, Inc. [FILE: GrassKey_Cenchrus.html] Genus Cenchrus – Page 9
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