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CPIE Notebook Project - Grasses of Hawai‘i and Guam Grass Key – Page 8

"Foxtail" Grasses

Foxtail grass example


Figure 8A. Typical foxtail inflorescences,
here of feathery pennisetum (Cenchrus polystachios)

The inflorescence of these grasses is a tight, cylindrical, spike-like panicle that tapers towards the tip and has numerous bristles that project outwards, thus resembling the bushy tail of a fox (see Figs. 8A & 8B). The bristles are typically soft, but may be sharp and stiff, forming burs that can catch on hair and clothing. For clarity, bristles are stiff, hair-like structures that, in these foxtail grasses, surround the base of each spikelet and (in Cenchrus) remain attached when the spikelet falls from the rachis. These differ from awns, which are terminal or nearly terminal bristlelike appendages on a floral bractlet. However, in Polypogon, the bristly appearance is actually due to numerous awns (one terminal on each glume).

spike-like panicle of buffelgrass

Our most common foxtail grasses are:

  • Buffelgrass [50]—covers leeward (dry) hillslopes (Fig. 8B) in Hawai‘i;
  • Fountain grass [51]—covers lava flows in Kona on Hawai‘i Island;
  • Elephant grass / Mission grass [52]—large, riparian (along streams) species in Hawai‘i and Guam.


            Figure 8B. Spike-like (cylindrical) panicle
            of Cenchrus ciliaris (buffelgrass)
            with hair-like projecting bristles.
  • [FOXTAIL GRASSES]

         
    44a (23) Inflorescence of S. verticillata Spikelets numerous on short branches arranged in whorls on the axis (a verticillate panicle), each spikelet with a single (sometimes 2), about 1/8 in (0.5 cm) bristle below. Leaves broad near middle, gradually tapering outward. Ligule ciliate. { Clumping, medium size annual. At maturity the spikelet bristles readily catch on each other and on clothing, forming entangled masses difficult to remove from fabric. Typically found in disturbed, dry to mesic environments (Fig. 8C). Bristly foxtail [HAW - NAT] barbed foxtail [GUM - NAT]
         Setaria verticillata (L.) P. Beauv.
    44b

    Inflorescence not as above; usually with only one spikelet per branch, the branches not obviously whorled on the axis or spikelets too condensed to determine. Bristles (or short awns) attend each spikelet, these either loosely catching on clothing or not (or may remain on the axis at maturity). Ligule ciliate or membranous .. .

    [45]
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    45a (44) Bristles surrounding the spikelet (as an involucre) remaining attached to the spikelet when spikelet separates from the rachis; bristles soft or hard. Spikelet a bur or bur-like, globose, narrow ovate, or spindle-shaped. Cenchrus spp. [48]
    45b

    Bristles fine, hair-like, either subtend (lie beneath) the spikelet or on glumes. Spikelet not a bur .. .

    [46]
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    46a (45) Dense "bristles" are actually fine awns arising on the glumes. Inflorescence a dense, cylindrical "foxtail", bluntly rounded at tip. Polypogon spp. .. .

    [50]
    46b Bristles radiate from base of spikelet. Inflorescence cylindrical to linear, tapering towards the tip, spike-like or with branches held vertical, close against the rachis .. . [47]
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    47a (46) Floret ellipsoid to lanceolate, but with both glumes extending well-beyond the floret. Numerous soft bristles surround base of spikelet. Leaves growing mostly from plant base up to 2 m (6 ft) or more in length. Ligule a ciliate membrane. Imperata spp. .. .

    [49]
    47b Spikelet ellipsoid (compressed, egg-shaped); glumes not conspicuously longer than floret; bristles antrorsely barbed. Ligule ciliate (a row of long hairs). Setaria spp. .. . [48]
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    [NOTE THREE CHOICES HERE]

    48a (47) Inflorescence of S. parviflora

    Perennial. Inflorescence 2 to 6 cm (3/4 to 4 in) long. Spikelets somewhat inflated; Upper glume nearly as long as floret, lower much shorter; lemma surface rugose { Medium size (or sometimes small) clumping grass found in disturbed areas. Yellow foxtail, perennial foxtail, mau‘u Kaleponi. [HAW - NAT] [?GUM - NAT]

          Setaria parviflora (Poir.) Kerguélen
    48b

    Perennial. Inflorescence 3 to 50 cm (1.1 to 18 in) long. Bristles often orange, present in groups of three. Glumes and lemma much as in S. parviflora { medium to large, densely cespitose, perennial grass, tolerant of flooded ground (see Figure 8E at bottom of page). [HAW - NAT] African bristle grass [?GUM - NAT]

      Setaria sphacelata (Schumach.) Stapf & C.E. Hubb ex M.B. Moss
    48c

    Annual. Very similar to S. parviflora and S. sphacelata; not a perennial. Yellow bristle grass [GUM - NAT]

      Setaria pumila (Poir.) Roem. & Schult.
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    49a (47) Panicle up to 30 cm (1 ft) long with brances up to 2 cm (1 in) long, appressed to the rachis and concealed by the spikelets. Two stamens per floret. Leaves with off-center, whitish mid-rib. { Widespread on Guam, spreading to form dense stands. USDA & HDA noxious weed. Cogongrass [GUM - NAT]
         Imperata cylindrica (L.) P. Beauv.

    49b Panicle up to 50 cm (1.5 ft) long with brances to 6 cm (2.4 in) or longer, ascending, not so concealed by the spikelets. One stamen per floret. { Resembling I. cylindrica, but larger. [GUM - NAT]
         Imperata conferta (J. Presl) Ohwi
    ~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
    50a (46) Glumes acute or rounded, rarely bifid at tip; awns on glumes short, between 1 and 4 mm long { Medium size, perennial tufted grass found in generally wet areas. Ditch polypogon [HAW - NAT]
      Polypogon interruptus Kunth
    50b Glumes typically bifid at tip; awns twice length of glume, between 4 and 7 mm long { Medium size, annual tufted grass found in generally wet areas. Rabbitfoot grass [HAW - NAT]
      Polypogon monspeliensis (L.) Desf.

    Uncommon species resembling or related to foxtails reported to be in Hawai‘i or Guam
      but not covered in this key; and a synonym:

      Polypogon fugax Steud.; Asian beardgrass (annual similar to P. interruptus).
      Polypogon viridis (Gouan) Breistr.; beardless rabbit's-foot grass
      Setaria gracilis Kunth (=S. parviflora)
    and possibly others sold as ornamentals [ORN].

     

    GRASS PHOTOS
    [CLICK ON THUMBNAIL TO OPEN AN ENLARGED IMAGE]

      Setaria sphacelata

    Fig. 8E. Roadside growth of Setaria sphacelata. (4.5 MB).


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