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A CPIE Notebook Project – Grasses of Hawai‘i and Guam Grass Key – Page 19
Tribe Andropogoneae
Key to Genus Bothriochloa Kuntze

Grasses of the genus, Bothriochloa are medium size, clumping grasses distinctive in the field with subdigitate racemes and long awns. Spikelets are paired, one sessile and the other pedicelled; only the sessile spikelet is awned. The pedicellate spikelet is either sterile or staminate; the sessile spikelet is fertile. Ligule is a membrane. Bothriochloa spp. are closely aligned with Dichanthium spp., a distinction being the "translucent medial groove of the [spikelet] pedicel" in Bothriochloa (and Capillipedium), requiring 20x or greater magnification to be seen (Faccenda, 2023). The key provided on this page more or less follows Faccenda's key combining the Hawaiian species of Bothriochloa and Dichanthium and reflecting species variation in the presence of pits on the glumes (see inset in Fig. 19A).

These grasses are commonly encountered in lawns and maintained roadside verges. Five species are recorded from the Hawaiian Islands (Clayton & Snow, 2010; Imada, 2012; Faccenda, 2023). None is listed from Guam (Raulerson, 2016) but two are listed from the Mariannas (Clayton & Snow) and might be encountered on Guam. All five species are introduced (alien) to both island groups.
[GENUS BOTHRIOCHLOA

      
110a (To last couplet104) First glume with a distinct pit (<1 mm across), visible to naked eye (if you have good eyesight; see Fig. 19B below) .. .

[111]
110b Glumes of spikelets lacking pits .. . [113]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
111a (110) Racemes subdigitate or arranged on the culm (axis) over a distance less than the length of a raceme .. . [112]
111b

Racemes arranged on the culm (axis) over a distance greater than the length of a raceme. Pedicels especially with many long hairs. Sessile spikelets 3 - 4.5 mm long { medium-size bunching grass, typically in disturbed sites and grassed verges. (See also couplet [116a]) [HAW - NAT] [FACU]; [?GUM - NAT] [FACU]

    Bothriochloa bladhii (Retz.) S. T. Blake
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
112a (111) Pitted beardgrass photo Pedicellate spikelets generally similar to sessile spikelets or very slightly reduced; pedicellate spikelets with or without a pit. Sessile spikelets 3–4 mm long. Racemes usually weakly erect to strongly divergent from axis { Extremely common small grass in lawns, road verges, and open dry to mesic lands. Pitted beardgrass [HAW - NAT] [?GUM - NAT]
    Bothriochloa pertusa (L.) A. Camus

Figure 19A. Bothriochloa pertusa inflorescences with fan-shaped arrangement of racemes arising close together and (inset) glumes with a small pit (clearly visible with a small hand lens; see Fig. 19B below).
112b

Pedicellate spikelets narrower than sessile spikelets and typically lacking a pit. Sessile spikelets 5–7 mm long. Ligule a membrane with sparse, minute cilia at apex. { Racemes usually held stiffly erect; resembles B. pertusa. Redleg grass [HAW - NAT] (See also couplet [117b])

    Bothriochloa macra (Steud.) S. T. Blake
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
113a (110)

Pedicellate spikelets narrower than sessile spikelets .. .

[114]
113b

Pedicellate spikelets similar in width to sessile spikelets .. .

[106]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
114a (113)

Pubescence of inflorescence of long hairs that obscure spikelets, whitish in color at maturity.. .

[115]
114b

Pubescence of inflorescence of hairs under 2 mm long, not obscuring spikelets. Inflorescence reddish or whitish in color .. .

[116]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
115a (114) Culm node with long hairs (villous), node may be dark purple in color. Sessile spikelet ovate, 4.5-7.3 mm long; pedicelled spikelet linear or lanceolate, 2-5 mm long. Ligule membranous without cilia (eciliate). { Uncommon, medium-sized, tufted perennial. Fuzzy top [HAW - NAT] [UPL]
    Bothriochloa barbinodis (Lag.) Herter
115b Culm nodes glabrous. Sessile spikelet ovate, 2.5-4.5 mm long; . {?Rare, medium-sized, tufted perennial. Fuzzy top [HAW - ?NAT]
    Bothriochloa laguroides (DC.) Herter
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
116a (114
  &
To last couplet111)		 Racemes attached along central axis from nodes spaced apart greater than length of a raceme. Pedicels especially with many long hairs. Sessile spikelets 3 - 4.5 mm long { common, medium-size bunching grass, in disturbed sites and grassed verges. (See also couplet [111b]) [HAW - NAT] [FACU]; [?GUM - NAT] [FACU]
    Bothriochloa bladhii (Retz.) S. T. Blake
116b Racemes attached along central axis over a distance less than length of a raceme .. . [117]
~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~
117a (116) Racemes 3 - 6 in number. Sessile spikelets 4.5–7 mm long. Ligule a membrane with sparse, minute cilia at apex. { Racemes usually held stiffly erect; resembles B. pertusa (See also couplet [112b]) [HAW - NAT]
    Bothriochloa macra (Steud.) S. T. Blake
117b Racemes 5 - 15 in number. Sessile spikelets 3.5–5 mm long, pedicelled spikelet similar in length.
    Bothriochloa ischaemum (L.) Keng

Plant very similar to Bothriochola pertusa but lacks pits on its glumes. The species is also similar to Dichanthium annulatum but differs in having more acute tips of its glumes and the difficult to discern transparent line running along the axis of the spikelet pedicels and inflorescence axis.

SUPPLEMENTAL PHOTOS
[CLICK ON THUMBNAIL TO OPEN AN ENLARGED IMAGE]
Pitted beardgrass showing pits

Fig. 19B. Closeup of pitted beardgrass (Bothriochloa pertusa) sessile spikelets showing distinctive glandular pits
(0.24 MB).

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