Oplismenus imbecillis

A ground-covering grass which can form large colonies to several metres wide, growing to about 0.3 metres tall. It has thin wiry stems which root at some notes.

It has a large natural geographic distribution in NSW, mainly coastal, growing from the Victorian border to the Queensland border, extending into the central and north-western slopes (seems to be absent from the southern and central tablelands) but present on the northern tablelands, as far west as Mt Kaputar National Park. The remainder of the distribution is a bit unclear as this genus is in a state of flux.

Please note: the Oplismenus genus is currently undergoing revision and all occurrences of this species may fall under O. hirtellus.

It tends to be found in wet and dry sclerophyll forest as well as rainforest, in sheltered areas such as creeklines and gullies on sandy to clay soils. It can grow alongside O. aemulus in some habitats. It can be a common species in temperate rainforest and littoral rainforest in NSW. In some habitats, it will form an extensive groundcover.

The family Poaceae is the grass family (any species outside this family should not be referred to as grasses). They are a group that a lot of us place in the “too-hard” basket but here are some simple facts about them: They are one of the largest groups of flowering plants, in the large monocotyledonous group (sedges, lillies, palms and orchids amongst others), with highly modified flowers and reduced perianth parts. Pollen from the anthers is generally wind-blown and is received by the female pistils. It is thought that grasses have evolved to dominate the planet over the last several 100,000 years, due to a general drying and cooling of many terrestrial areas. Hence, we have the grass-prairies of America, Africa and Australia, as well as other areas with a general reduction in vegetation like rainforests. It is worth remembering that humanity relies heavily on the seeds of 3 grass species for food; namely Wheat (*Triticum aestivum), Corn (*Zea mays) and Rice (*Oriza sativa) – not to mention fodder for agricultural meat.

Identification of grasses can be difficult if one is to plunge ‘in-depth’ but many genera can be identified by the appearance of their inflorescences. Different terminology is applied. Petals and sepals do not apply to flowers but rather structures such as glumes which are bracts that generally support the base of ‘spikelets’ (clusters of flowers or single flowers) with flowers generally called ‘florets’. Florets typically consist of a palea and a lemma (two joined structures which house the stamens and carpels). Florets can be bisexual or unisexual or sterile. In some genera, glumes are absent. Inflorescence structures are generally familiar, i.e. panicles, racemes, spikes etc).

There are a range of habits such as tussocks or clumping grasses (Poa, Themeda, Cymbopogon etc), to large clumping and running bamboos (world’s largest grasses) and stoloniferous grasses – those that creep prostrate over the ground using stolons (eg: turf grasses such as Kikuyu (*Cenchrus clandestinus) and Oplismenus aemulus).

Grasses produce simple leaves, usually made up of a blade and sheath with accompanying parts such as auricles, ligule and collars (where the blade joins the sheath).

Oplismenus spp. have wiry stems with alternate and simple leaves. In this species, leaves (or blades) are to 50 mm long and 7 mm wide, lanceolate to subulate in shape and tapering strongly to a fine point, with 10 to 15 fine nerves; with the base of the leaf clasping the stem; mostly mid green to dark green (often dark green) in colour; with entire margins.

The stems of the flowering heads in grasses are called culms. In this species, spikelets are simply produced at the terminals of leafy stems, but can be called culms; to 0.3 metres tall. Overall, a terminal panicle is produced of separate racemes, each raceme is at right angles to the stem, to about 15 mm long by only 2 millimetres wide, consisting of spikelets to about 2 to 3 mm long. The spikelets are awned at the apex and typically green in colour, sometimes with red and paler tones (awns generally red). Each spikelet contains about 2 florets which eventually ripen to produce seed about 2 mm long.