Aristea spiralis is a slender, herbaceous, evergreen, rhizomatous perennial that grows up to 500 mm tall. It is often found in small clumps. The stems are usually unbranched, flattened and winged on the edges. The narrow, 4–7 mm wide, sword-shaped leaves have a soft texture and translucent, angular margins. Plants flower in spring, between August and November. Flowers are placed in two to seven lateral flower clusters on each stem, with each cluster consisting of four, or rarely two, flowers. Greenish spathes (bracts) with translucent margins sheath each flower cluster and dry, membrane-like bracts sheath each flower. The spathes are 33–45 mm long and the bracts somewhat shorter. The half to fully nodding flowers range from white to pale blue in colour and have linear or V-shaped purple markings at the tepal bases. They are often placed on only one side of the stem. The tepals range from 28 to 35 mm long, the inner slightly larger than outer. The filaments are 22–26 mm long or rarely only half as long and the anthers 4.5–6.3 mm long. The 3-lobed ovaries are elongate and 12–15 mm long, while the style is 30–35 mm long with spreading, deeply fringed stigma lobes. Triangular-columnar seeds are placed in elongate, deeply 3-lobed, woody capsules, 30–50 mm long.

Fig. 2. An Aristea spiralis plant in flower. Photo by johnharoldwilson

Plants of this species can be distinguished by a combination of their large, half to fully nodding flowers that are white to blue with light purple markings near the bases of the tepals. The stamens and style extend horizontally, and most populations have notably long filaments (22–26 mm long), whereas allied species have filaments up to only 6 mm long.