A cormous geophyte 15-20 cm high. The stem is usually unbranched and plants have a very slender and delicate habit. Corms are 8-12 mm in diameter with light brown coarsely fibrous netted tunics. Leaf single, linear, narrowly channelled, usually exceeding the inflorescence, 4-8 mm wide with a smooth surface. Leaves usually dry towards the tip. Spathes herbaceous, dry and brown above, with a sharply pointed tip. Flowers white, outer tepals with yellow nectar guides outlined with dark blue. Usually stripe extends down the tepal and blue to purple spots present around and below the nectar guides. Style branches about 10 mm long with erect crests. Flowering September to October and most profusely in the first year after a fire.

Moraea longiaristata 's distinguishable characteristics are the white flowers with large outer tepals and long filiform inner tepals. Its closest relative is Moraea barnardii, which is another range-restricted species occurring about 5 km south of Caledon. The difference between them is the lack of the long inner tepals in M. barnardii. In most other respects these species are very similar.