Oropetium, Trinius, 1820

Shinde, Rajendra D., Landge, Shahid Nawaz, Kulloli, R. N. & Chorghe, Alok R., 2023, Oropetium almeidanum (Poaceae: Chloridoideae): a new species from The Thar Desert, Rajasthan, India, Phytotaxa 579 (4), pp. 267-277 : 275

Key to the species of Oropetium in the world

1. Rhachis fragile, readily or tardily disarticulating into spiculated segments (African & Arabian species; exceptionally including O. almeidanum ) ......................................................................................................................................................................................2

1. Rhachis not fragile, not disarticulating into spiculated segments, apparently tough and persisting ( Indian species)........................5

2. Annual; butt sheaths lacking at the base of the culm ...................................................................................................... O. aristatum

2. Perennial; butt sheaths persistent at the base of the culm ..................................................................................................................3

3. Spikes straight or curved, never flexuous; rhachis bilaterally flattened not triangular in transverse section, spikelets in two subopposite rows; upper glume apex acute or long-acuminate (apex 2.5 mm long), never awned ........................................................4

3. Spikes straight or flexuous; rhachis not bilaterally flattened, triangular in the transverse section, spikelets in two rows disposed just side by side (adjacent); upper glume apex acuminate to long awned (awn 2–18 mm long)........................................... O. minimum

4. Spikelets 2.0–3.0 (–4.0) mm long; upper glume nerves not ribbed, apex acute; lemma 1.5–2.0 (–2.5) mm long; palea apex without excurrent keel nerves; caryopsis 1.0– 1.5 mm long ............................................................................................................ O. capense

4. Spikelets 4.0–6.0 mm long; upper glume 4.0–5.3 × 0.8 mm, nerves strongly ribbed, apex long-acuminate; palea apex with two conspicuous excurrent keel nerves and broadly winged; caryopsis up to 1.8 mm long............................................. O. almeidanum

5. Annual; spikes 1.0– 3.5 cm long; one flowered spikelet without a rachilla extension .......................................................................6

5. Perennial; spikes more than 4.0 cm long; usually one flowered, sometimes also two flowered spikelet then with a conspicuous rachilla extension................................................................................................................................................... O. roxburghianum

6. Butt sheaths absent at the base of the culms; spikes terete, not with a distinct saw-toothed appearance, up to 1.5 cm long, subtended by a spathaceous sheath at the base; lemma villous on the dorsal side......................................................................... O. villosulum

6. Butt sheaths persistent, somewhat fibrous at the base of the culms; spikes laterally compressed, with a distinct saw-toothed appearance, 1.5–3.5 cm long, not subtended by a spathaceous sheath at the base; lemma glabrous on the dorsal side...................... ....................................................................................................................................................................................... O. thomaeum