Astrebla

Astrebla F. Muell.,. Flora Australiensis
7: 602 (1878).

Derivation:.
From Greek, a (not) and streblos (twisted), alluding to the
straight awns. The common name is in honour of Sir Thomas Mitchell who
collected the first recorded specimens near Condobolin, N.S.W. in 1836.

Taxonomic
revisions, nomenclatural references:. C.E.Hubbard, Bull. Misc. Inf., Kew 7: 256–266
(1928); F.X.Joswick, Aust. J. Bot. 17: 359–374(1969).

Key references
(keys and floras):. G.Bentham, Flora Australiensis 7: 602–603
(1878); C.A.Gardner, Flora of Western Australia 1 Gramineae
201–205 (1952); M.Lazarides, Flora of Central Australia 447–448 (1981);
J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 118–119 (1983);
J.P.Jessop, Flora of South Australia 4: 1856 (1986); M.Lazarides,
F.Quinn and J.Palmer, Flora of the Kimberley Region 1127–1128 (1992);
B.K.Simon, Key to Australian Grasses 74 (1993); D.Sharp and B.K.Simon, AusGrass
(2002); K.Mallet (ed.), Flora of Australia 44B: Poaceae 3:
452–457 (2005); J.P.Jessop, Grasses of South Australia 338–341 (2006);
S.W.L.Jacobs, R.D.B.Whalley & D.J.B.Wheeler, Grasses of New South Wales,
4th Ed, 135–137 (2008).

W.D.Clayton & S.A.Renvoize, Genera Graminum
(1986), genus (386).

Native, endemic. 4
species. WA, NT, SA, Qld, and NSW.

Habit.
Perennial, tufted. Leaf blades narrow. Ligule a fringe of hairs.

Inflorescence.
Inflorescence a single spike or of spicate main branches or a single raceme
(with short pedicels), a single raceme or spike (rarely paired), digitate or
non-digitate (when the racemes solitary).

Spikelets.
Spikelets laterally compressed, more than 2 flowered, with 2 or more fertile
florets, awned, solitary, sessile to subsessile or pedicelled (with short
pedicels); with naked rachilla extension. Fertile spikelets disarticulating
above glumes.

Glumes. Glumes
unequal to more or less equal, shorter than adjacent lemmas or long relative to
adjacent lemmas, pointed (acute), awnless, keeled, similar (membranous to
papery). Lower glume 2–9 nerved. Upper glume 7–13 nerved.

Florets.
Fertile florets (2–)3–7. Lemmas silky villous, decidedly firmer than glumes
(leathery), not becoming indurated, incised, deeply cleft, awned, 3–11 nerved,
basally hairy, not keeled. Awns 1 (by terminal extension of the median lobe) or
3 (by extensions of all three lobes), the median similar in form to laterals
(when laterals present), from a sinus or apical, non-geniculate, often curved,
hairless, much shorter than body of lemma to much longer than body of lemma.
Lateral awns when present shorter than median to about equalling median. Palea
entire (acuminate), 2 nerved. Palea keels wingless (ciliate). Distal incomplete
florets 0–5, underdeveloped. Lodicules 2. Stamens 3. Grain small, ellipsoid,
longitudinally grooved, compressed dorsiventrally or terete. Hilum short.
Embryo large.

Kranz Anatomy.
C₄, biochemical type NAD-ME (4 species).

2n = 40.

Habitat.
Xerophytic. Dry sandy grassland. Species of open habitats.

Classification.
Chloridoideae; Cynodonteae.

Notes. An
isolated genus, with no obvious relative in Cynodonteae, but some resemblance
to Tetrapogon (Clayton and Renvoize, 1986). Although the species are
readily distinguished, probable interspecific hybrids occur but are mostly
sterile. Self-fertilizaton under experimental conditions has been reported for
all four species, and evidence of cleistogamy seen in all species except A.
squarrosa. Mitchell grasses are restricted to the black, grey, brown and
red cracking clay soils, and are usually a major element in grassland
communities on these soils. They are well known for their drought resistance,
persistence and fodder value. In many areas of Qld, there is a cyclic
oscillation between Mitchell Grass dominance and Queensland Bluegrass (Dichanthium
sericeum) dominance, according to the particular sequence of wet or dry
seasons (Flora of Australia 44B, 2005).