| Onion
twitch (Arrhenatherum elatius) is a distinctive,
common and widespread weed species in Tasmania, mostly in
disturbed areas. It is a large, loosely tufted grass. The
distinctive features are that the plant has a line of bulbs
at the base of the stem, and the flowers. The inflorescence
is a loose panicle that tends to bend over near the top. The
spikelets are widely gaping when mature and about 5-10 mm
long, the glumes are transparent, one flower in the floret
has an obvious awn about 15mm long. The awn is bent near the
middle and attached in bottom third of the lemma. The awn on
the other flower in the floret is inconspicuous.
This species can be confused with another common weed,
oatgrass (Avena spp). Avena
has similar inflorescence and growth habit, though the
spikelets are distinctly larger (with glumes at least 15mm
long, compared to less than 10mm in Arrhenatherum).
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University of Tasmania
