1Lamina covered with stellate hairs
1'Lamina with (sometimes umbrella-shaped) scales, simple hairs, or glabrous
2Lamina simple, sori round or linear
2'Lamina variously dichotomously divided, sori forming large spreading patches.
3Venation open, if anastomosing, then with 1-3 rows of areoles without included veinlets or with a single excurrent included veinlet, the lamina pinnately divid-ed
3'Venation anastomosing, forming a complex, reticulate pattern, recurrent free vein- lets usually present
4Venation open
4'Venation anastomosing
5Rhizome scales fully clathrate (widespread)
5'Rhizome scales not clathrate, or indistinctly clathrate in the acumen only (Borneo)
6Ant ferns with swollen, hollow or laterally expanded rhizome, rhizome scales appressed, peltate and rounded; or very small or absent.
6'Not ant ferns, rhizome not hollow or expanded, if strongly thickened then rhizome scales elongated
7Rhizome scales at least partly clathrate
7'Scales on rhizome and/or fronds isotoechous (not clathrate)
8Sporangia in elongated coenosori
8'Sori round or elongated, but not forming coenosori
9Fertile fronds or frond parts wide, with transverse coenosori.
9'Fertile fronds or frond parts narrowed, with longitudinal coenosori
10Fronds monomorphic, coenosori on an apical narrowed frond part (‘spike’).
10'Fronds dimorphic, coenosori on separate, narrowed fronds
11Clathrate scales present between the sporangia, rhizome filiform, to 1.1 mm thick, long-creeping
11'No clathrate scales present between the sporangia, rhizome usually thicker.
12Sori stipitate on slender stalks on the lamina margin
12'Sori on the lamina surface, sometimes deeply sunken
13Sori marginal (L. longifolius)
13'Sori costal to medial
14Young sori covered with peltate scales
14'Young sori not covered with peltate scales
15Sori in a single row between midrib and margin, singly between each pair of the veins
15'Sori in several irregular rows between midrib and margin (at least an irregular second row always present), 1-3 rows between each pair of veins.
16Rhizome c. 1 mm thick, filiform, sori in a single row between costa and margin.
16'Rhizome over 1 mm thick, not filiform, rarely thinner, then sori in several rows between costa and margin
17Lamina simple, trilobed, pinnatifid or pinnate, no articulation pad, abscission vein or nectaries present
17'Lamina pinnatifid or pinnate, with either a distinct articulation, abscission vein between lobes or nectaries near the base of the lobes (or with all three)
18Lamina trilobed, fertile fronds with linear coenosori
18'Lamina simple or pinnate-pinnatifid, if trilobed then with separate sori
19Lamina with erect, scattered uniseriate hairs, sori irregularly scattered.
19'Lamina glabrous or with very short, appressed glandular hairs, rarely with erect hairs, then sori in two rows between each pair of veins
20Lamina pinnatifid or pinnate with conspicuous nectaries near the base of the pin-nae; large plants, usually over 0.5 m high
20'Pinnae without nectaries at the base, small plants less than 0.5 m high.
21Separate, usually sterile, nest-forming base fronds present, distinctly shorter and less deeply dissected than the foliage fronds, apex of foliage fronds nearly always aborted (the insufficiently known Aglaomorpha nectarifera, should it be rediscovered, may also key out here)
21'Separate base fronds absent (sterile fronds, if present, large and deeply dissected), apical pinna normally developed