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M. ambigua, M. minutiflora, M. tenuissima, M. effusa and M. macrochaeta form a group of similar species with rare intermediate forms occurring between neighbouring species. The weakest delimitation is between M. minutiflora on the one side and M. ambigua, M. effusa and M. tenuissima on the other. M. ambigua is a very variable species. Subsp. ambigua and subsp. longicauda differ in spikelet morphology and habit with many intermediate forms occurring. Forms of subsp. longicauda may approach M. longiseta, but the nervation and hairiness of the superior glume are reliable characters for identification. Rare specimens with the keels of the inferior palea ciliate, possibly introgression products from M. repens, have been described as Rhynchelytrum bequaertii.
Inferior glume 0.4–1.2 mm. long, ovate, 0–1-nerved, inserted close to the superior; superior glume 7-nerved, usually hairy, emarginate to bilobed with an awn (0.1)0.5–6.8(8.3) mm. long.
Inferior floret male or barren, its lemma 5-nerved with an awn (0.3)2–13(14) mm. long, equalling the superior glume; palea absent or when present scabrous on its keels.
Culms (30)60–120(150) cm. high, erect or rarely geniculately ascending.
Leaf laminae (3.5)5–30 cm. long, 2–8(11) mm. wide, flat or involute.
Spikelets (2)2.4–4.4(5.2) mm. long, narrowly ovate.
Caespitose or rarely tufted perennial.
Panicle 9–25 cm. long, narrowly ovate.
Pedicels with a few long hairs.
