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CPIE Notebook Project - Key to the Grasses of Hawai‘i Page 8

Common "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 bristles on a floral bract. However, in Polypogon, the bristly appearance is 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);
  • Fountain grass [51]—covers lava flows in Kona on Hawai‘i Island;
  • Elephant grass [52]—large, riparian (along streams) species.

    Figure 8B. Spike-like (cylindrical) panicle
    of Cenchrus ciliaris with hair-like
    projecting bristles.
  • ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    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. { 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 areas. Bristly foxtail. (Fig. 8C) [NAT]

    Setaria verticillata (L.) P. Beauv.

    Inflorescence not as above; usually with only one spikelet per branch, the branches not obviously whorled on the axis. Bristles attend each spikelet, these either loosely catching on clothing or not

    45a (44) Bristles remaining on rachis when spikelets fall. Spikelet ellipsoid (compressed, egg-shaped). [46]

    Bristles surrounding the spikelet (as an involucre) remaining attached to the spikelet when spikelet separates from the rachis. Spikelet a bur or bur-like, globose, narrow ovate, or spindle-shaped. Cenchrus spp.

    46a (45) Inflorescence 2 to 6 cm (3/4 to 4 in) long. { Medium size (or sometimes small) clumping grass found in disturbed areas. Yellow foxtail, perennial foxtail, mau‘u Kaleponi. [NAT]
    Setaria parviflora (Poir.) Kerguélen

    Inflorescence 3 to 50 cm (1.1 to 18 in) long. { medium to large, densely cespitose, perennial grass. [NAT]

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

    Uncommon species in Hawai‘i resembling foxtails but not included in key [NAT]:

      Polypogon monspeliensis (L.) Desf. – beard grass
      Polypogon interruptus Kunth – Ditch rabbit's-foot grass
    and possibly a few others sold as ornamentals [ORN].



    Setaria sphacelata

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

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