Table 1 Comparative morphology of Trigonochilum cimiciferum, T. koenigerii, and T. midas

Pseudobulbs

Rounded-ovoid, 5–8 × 1.5–2.5 mm

Oblong-cylindrical, 7 × 4 cm

Ovoid, 4–10 × 2–3 cm

Leaves

Narrowly ovate, 20–40 × 1.5–3 cm

Linear-oblanceolate to linear-oblong, 38 × 3.5 cm wide

Elongate-obovate, acuminate, up to 65 × 2 cm

Pedicellate ovary

10–30 mm

About 28 mm

Up to 20 mm

Flower

Brownish-yellow with brown spots, with yellow lip callus

Brown with yellow lip callus

Almost completely white with whitish to yellow lip callus

Sepals

Spathulate to rotundate, rounded-acute, acute or acuminate

Unguiculate to spathulate, elliptic-oblanceolate, subacute or subobtuse

Spathulate, ovate, acuminate

Petals

Subsessile, obovate-elliptic to narrowly obovate or oblanceolate, acute

Subsessile, oblong elliptic-obovate, acute

Subsessile, ovate, acuminate

Lip

Ovate, ovate-triangular to elliptic-obovate; disc with a fleshy callus in the basal half

Widely triangular to ovate-triangular; disc with a fleshy, complicated callus in the basal 2/3 and two subglobose thickenings at the base

Cordate to truncate; callus a central, longitudinal, fleshy structure, extending from the base to 2/3 of the disc length, terminating in digitate knobs or denticles