"Foxtail" Grasses

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).

Our most common foxtail grasses are:

Buffelgrass [50]—covers leeward (dry) hillslopes (Fig. 8B) in Hawai‘i;

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] [FACU] barbed foxtail [GUM - NAT]

   Setaria adhaerens (Forrsk.) Chiov.

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 .. .

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

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] [FACU] [?GUM - NAT]

    Setaria parviflora (Poir.) Kerguélen

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] [FAC] African bristle grass [?GUM - NAT]

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

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

Setaria pumila (Poir.) Roem. & Schult.

   Imperata cylindrica (L.) P. Beauv.

Cogongrass (both species found on Guam) is regarded as one of the ten worst weeds in the world (Global Invasive Species Database, 2021 cited in Faccenda, 2022) and was observed as an ornamental in Kane‘ohe, O‘ahu in 2007; since eradicated). May be sold as an ornamental cultivar distinguished by the unique characteristic of having the leaves colored red above the middle, green below; and having some leaf midveins located off-center.

   Imperata conferta (J. Presl) Ohwi

Polypogon fugax Steud.

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 interruptus Kunth (= P. fugax in Hawai‘i) — Faccenda, et al., 2024.
Polypogon viridis (Gouan) Breistr.; beardless rabbit's-foot grass
Setaria distans (Trin.) Veldkamp — Faccenda, 2022; Faccenda, 2023.
Setaria gracilis Kunth (=S. parviflora)
Setaria italica (L.) P. Beauv. — Faccenda, 2022.
Setaria verticillata (L.) P. Beauv. (= S. adhaerens)

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