Plants 150-500 mm high. Corm 15-18 mm diam.; tunics of coarse, netted fibres. Stem usually with 2 to 5(-12) short, filiform, branches 2-6 mm long, subtended by scale-like truncate bracts and prophylls ± 1 mm long. Leaves usually 4 (or 3), lower 2 with expanded blades, broadly lanceolate to falcate, ± 1/4-1/2 as long as stem, 8-15 mm wide; margins thickened, pale, hyaline when dry; upper two leaves partly to entirely sheathing, uppermost reaching to between upper 1/3 of stem and base of spike. Main and lateral spikes 1-to 3-flowered; bracts membranous, translucent, becoming brown and dry distally, 8-12 mm long, outer 3-veined and shortly 3-toothed, inner 2-veined and forked at tip. Flowers mostly half nodding, blue-mauve, tepals dark red at base, black in wide part of tube, filaments and style dark purple, faintly acrid scented; perianth tube ± 3 mm long, funnel-shaped; tepals obovate, 12-15 x 6-8 mm, ascending to form a wide cup. Filaments purple, 5-7 mm long, exserted ± 3-5 mm; anthers 4-5 mm long, parallel, contiguous, yellow; pollen yellow. Style purple, dividing opposite middle of anthers, branches ± 2 mm long, purple below, becoming pale blue distally.
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Like I. marginifolia but flowers always blue-mauve with dark blackish centre edged with red, filaments and style branches blackish, filaments 4 mm long (vs. 5-6 mm).