Panicum trachyrhachis Benth. Fl.
Austral. 7: 490 (1878).
Classification. (GPWG 2001) : Subfamily
Panicoideae. Paniceae.
Type of Basionym or
Protologue Information: ST: Elsey s.n., Australia: Port Darwin LT: Schultz
343, Australia: Port Darwin (K). LT designated by Veldkamp, Blumea 41: 207
(1996). ST: M'Kinlay s.n., Australia: Arnhem's Land.
Recent synonyms:
Panicum robustum B.K.Simon, Austrobaileya 3: 598 (1992).
Key references
(books and floras): [2002] D.Sharp & B.K.Simon, AusGrass, Grasses of
Australia.
Habit. Annual.
Rhizomes absent. Stolons absent. Culms erect, stature robust to moderate,
60–180 cm tall, 3–6 -noded. Mid-culm internodes glabrous. Mid-culm nodes
glabrous. Lateral branches sparsely branched. Leaf-sheaths smooth, glabrous on
surface or hairy. Leaf-sheath auricles absent. Ligule a fringed membrane or a
fringe of hairs, a ciliate membrane, 1.2–3 mm long. Leaf-blades linear, flat or
involute, 12–45 cm long, 3–7 mm wide. Leaf-blade surface smooth or scabrous,
glabrous.
Inflorescence.
Inflorescence compound, a panicle. Panicle ovate, 30–65 cm long, evenly
furnished.
Spikelets.
Spikelets pedicelled. Fertile spikelets 2-flowered, the lower floret barren
(rarely male), the upper fertile, comprising 1 basal sterile florets,
comprising 1 fertile floret(s), without rachilla extension, elliptic, laterally
compressed, 3.75–4 mm long. Rhachilla internodes elongated between glumes.
Glumes. Glumes
thinner than fertile lemma. Lower glume lanceolate, membranous, without keels,
3–5 -nerved. Lower glume apex awned. Upper glume lanceolate, 2.9–3.7 mm long,
membranous, without keels, 7 -nerved. Upper glume apex muticous or awned. Florets.
Basal sterile florets 1, barren, without significant palea. Lemma of lower
sterile floret 100 % of length of spikelet, membranous, 9 -nerved, mucronate.
Fertile lemma 2.1–2.4
mm long, without keel. Lemma apex muticous. Anthers 3.
Continental
Distribution: Tropical Asia and Australasia.
Australian
Distribution: Western Australia, Northern Territory, Queensland.
Western Australia:
Gardner. Northern Territory: Darwin & Gulf, Victoria River. Queensland:
Burke, Cook, North Kennedy.
Notes.
The lower leaves are terete with spongy tissue on the adaxial surface whereas
the upper leaves lack this modification. The upper floret has a poorly formed
stipe at the base. At maturity, this stipe swells and resembles that found in Yakirra.
The base of the palea of the upper floret protrudes as in Ichnanthus.
Close relatives of P. trachyrachis include P. queenslandicum, P.
seminudum and Y. nulla.
New Guinea. In
tropical and subtropical sub-humid woodlands, coastal grasslands, and tropical
sub-humid grasslands. Occurs in semi-aquatic or aquatic habitats in the tropics
and subtropics of northern Australia and New Guinea. Frequently grows as a weed
in rice paddocks. Flowers throughout the year.
