Moraea polystachya and M. venenata are both perennial geophytes, the leaves and aerial stems dying back to the large dark-coated corm during the period of dormancy following flowering and seeding.

The two species are not easy to distinguish: the leaves are 3-5 or 6 in number, long and strap-shaped, flat or slightly U-shaped and slightly twisted spirally; in Moraea polystachya they are about 6-12 mm wide with unthickened margins, whereas in M. venenata they are 10-30 mm wide, often with the lowest two close together to form a cup-like structure at the base of the stem and with the margins thickened and yellowish.

The flowering stem averages about 0.8 m tall in M. polystachya and 0.25 m tall in M. venenata, although well-grown plants can be much taller. The flowering stem is many-branched at the top, and although each flower lasts only one day, a succession of flowers is produced so that the flowering period may last for six to eight weeks.

The upright flowers are relatively unspecialized in the genus, with an outer ring of three large more-or-less spoon-shaped tepals, and an inner ring of three smaller and narrower tepals. In the outer or both rings, the tepals curve outward or downward from the point where they broaden. As mentioned above, flower colour ranges from dark blue through violet (with pinkish tones) to white with fine blue lines, to pure white. One or both tepal rings have yellow to orange nectar guides at the base of each tepal. M. polystachya has smaller flowers, with the outer tepals about 50 mm long, in contrast to those of M. venenata where the outer tepals may be up to 60 mm long. In the centre, is the self-coloured (same colour as tepals), complex expanded style structure, similar to that of the cultivated iris, which crowns the ovary and hides the stamens. In M. polystachya the ovary usually protrudes from the floral bracts and develops into a rounded capsule, 11-16 mm long; in M. venenata, the ovary is concealed by the floral bracts and develops into an oblong capsule, 16-20 mm long. The capsule splits open when mature to release many small angular, pale brown seeds.