| 1 | Leaves distinctly petioled. |
| 1' | Leaves not petioled. |
| 2 | Flowering stems central (arising from the centre of the shoot on which the normal leaves are borne), triquetrous, rough-hairy especially on the angles. Inflorescence capitate, with 8-50 spikelets, the lower 1-2 involucral bracts more or less foliaceous, tailed, overtopping the inflorescence. |
| 2' | Flowering stems (scapes) lateral (developing from shoots in the axils of the leaves or below the leaves), terete or trigonous, the base clothed with bladeless, scale-like sheaths. Inflorescence either a single spikelet or capitate, in the latter case involucral bracts not foliaceous, glume-like, not overtopping the inflorescence. |
| 3 | Inflorescence normally a single terminal spikelet, sometimes with 1-2(-4) sessile or peduncled spikelets in the axils of the lower glumes. Scapes glabrous and smooth, (½-)1-2 mm thick. Leaves (½-)3-7 cm wide |
| 3' | Inflorescence always capitate, with 8-16 spikelets. Scapes rough-hairy (ultimately glabrescent), (2-)3-6 mm thick. Leaves 6-12 cm wide |
| 4 | Flowering stems central (arising from the centre of the shoot on which the normal leaves are borne), triquetrous, nearly always with 1-2 cauline leaves. Inflorescence capitate, with several to numerous spikelets, surrounded by foliaceous involucral bracts at least one of which much overtops the inflorescence. |
| 4' | Flowering stems (scapes) lateral (developing from shoots in the axils of the leaves or below the leaves), terete or trigonous, the base clothed with bladeless scale-like sheaths; scapes sometimes very short to almost lacking. Inflorescence either a single spikelet or capitate, in the latter case involucral bracts not foliaceous, glume-like, not overtopping the inflorescence. |
| 5 | Flowering stems stout to very stout, 4-8 mm thick. Leaves (2-)4-6 cm wide. Inflorescence with many to numerous spikelets. Spikelets 1½-3(-4) cm long, flowers 10-15 mm. |
| 5' | Flowering stems rather slender, 1½-2 mm thick. Leaves 0.6-1.1 cm wide. Inflorescence with 5-10 spikelets. Spikelets 1-1½ cm long, flowers 5-7 mm |
| 6 | Apex of the leaves acute, but not caudate. Leaves with 3 prominent nerves, the latter all very scabrid on their raised surface almost from the base to the apex of the leaves |
| 6' | Apex of the leaves ending in a tail-like, triquetrous, scabrid acumen. Leaves with 1-several prominent nerves, but mostly only the midnerve distinctly scabrid on its raised surface. |
| 7 | Stem elongate, densely leafy, up to 50 cm long, producing in the leaf-axils solitary, subsessile spikelets. |
| 7' | Stem short, not carrying a number of solitary, subsessile spikelets in successive leaf-axils. |
| 8 | Fruit with fleshy exocarp, berry-like, distinctly shrivelled when dried, yellow or orange (New Guinea). |
| 8' | Fruit with dry exocarp, smooth to slightly rugulose, brown to blackish. |
| 9 | Inflorescence composed of several very densely packed spikelets at first sight hardly distinct from one another, and surrounded by some erect involucral bracts much firmer in texture than the pellucid, indistinctly nerved flower-bearing glumes, the whole simulating a single spikelet. |
| 9' | Inflorescence either a single spikelet or composed of several to numerous distinct spikelets, in the latter case involucral bracts not strikingly different in texture from the coriaceous or chartaceous, distinctly nerved glumes. |
| 10 | Inflorescence (2-)2½-4½ cm long. Flowers c. 20 mm long |
| 10' | Inflorescence c. 1-1½ cm long. Flowers 5-8 mm long. |
| 11 | Leaves broadly linear, 2½-4½ cm wide, abruptly contracted into the tail. Involucral bracts suborbicular |
| 11' | Leaves linear, ½-1 cm wide, very gradually narrowed towards the apex. Involucral bracts elliptic or ovate |
| 12 | Inflorescence always capitate, consisting of several to numerous distinct spikelets. |
| 12' | Inflorescence normally consisting of a single terminal spikelet, sometimes (on the same plant) some of them with 1-4 lateral sessile or peduncled spikelets added. |
| 13 | Bases of the leaves castaneous. |
| 13' | Bases of the leaves stramineous to light brown. |
| 14 | Leaves 1-3 cm wide. Involucral bracts 1-2 cm long. Glumes 9-12 mm long. Style usually bifid. Nut c. 5 by 3 mm |
| 14' | Leaves 7-9 mm wide. Involucral bracts very short, 2-4 mm long. Glumes 3½-4 ram long. Style trifid. Nut 3-3½ by 1½ mm |
| 15 | Glumes reddish brown, strongly nerved, almost ribbed when dry. Outermost flower-scales winged on the keel. Leaves with only the midnerve prominent |
| 15' | Glumes stramineous, much less conspicuously nerved. Outermost flower-scales not winged. Leaves with 3 more or less prominent nerves |
| 16 | Bases of the leaves castaneous to blackish. |
| 16' | Bases of the leaves stramineous or light brown, in M. graminea with castaneous margins. |
| 17 | All spikelets sessile, triquetrous. Outer glumes sharply keeled. Flowers 15-30 mm long. Nut c. 10 mm long, the 3-4 mm long conical beak included |
| 17' | Spikelets at least partly peduncled. Outer glumes concave. |
| 18 | Leaves somewhat plicate lengthwise along several distinct lateral nerves |
| 18' | Leaves with 1 or 3 prominent nerves. |
| 19 | Leaves very shining above, smooth, very densely crowded, strikingly 3-ranked, the rows very prominent and fan-like at the base; midnerve prominent beneath, 2 whitish lateral nerves somewhat prominent above. Scapes scabrous, or (at length?) glabrescent. |
| 19' | Leaves when dry finely transversely wrinkled by numerous cross-nervules, not strikingly 3-ranked; midnerve prominent beneath, no prominent whitish lateral nerves. Scapes smooth. |
| 20 | Spikelets 6-10 mm long. Nut 2¼-2½ mm long. Leaves 2-4 mm wide |
| 20' | Spikelets and nuts much longer. Leaves at least 5 mm wide, usually much wider. |
| 21 | Nut lageniform (subglobose in the centre, distinctly beaked, constricted in the lower part and then conspicuously widened into the truncate base). Leaves remotely scabrous on the margins. Scapes usually long, (10-)45-90 cm |
| 21' | Nut ellipsoid, obovoid, or pyriform. Leaves with densely serrate-scabrous margins (except in M. borneensis). Scapes often shorter. |
| 22 | Leaves conspicuously tessellate or with numerous prominent cross-nervules. |
| 22' | Leaves not tessellate. |
| 23 | Leaves subcoriaceous, with 3 prominent nerves, conspicuously narrowed towards base and apex. Margins of the leaves scabrid only in the upper part. |
| 23' | Leaves mostly thickly coriaceous, with only the midnerve prominent, hardly narrowed towards the base, gradually narrowed upwards. Margins of the leaves serrate-scabrous throughout |
| 24 | Leaves very densely crowded, strikingly 3-ranked, very prominently equitant and fan-like at the base. Upper surface of the leaves scabrous just below the tail. Spikelets trigonous when young |
| 24' | Leaves not strikingly 3-ranked, not scabrous on the upper surface. Spikelets terete. |
| 25 | Leaves somewhat plicate lengthwise along several distinct lateral nerves. |
| 25' | Leaves with 1 or 3 prominent nerves. |
| 26 | Leaves dark green, 1-2 cm wide. Scapes (2-)10-40 cm long. Inflorescence always a single spikelet. Outermost flower-scales not winged |
| 26' | Leaves pale glaucous, (2-)3½-5 cm wide. Scapes 2-4(-10) cm long. Inflorescence not rarely with 2-5 spikelets. Outermost flower-scales winged on the keel. |
