Thereianthus is a small genus of 11 cormous plants from the Southwestern Cape of South Africa in the Iridaceae family. They are unusual for a winter rainfall climate as most species bloom in the dry warm summer months. Flowers are blue, purple, or white, spirally inserted, and growing in spikes. This genus is related to Micranthus but lacks the membraneous bracts and two-ranked spikes of that genus. The flowers are also shorter.
Thereianthus bracteolatus (Lam.) G.J.Lewis is found on dry sandstone slopes in the north and southwest Cape. It has blue, purple or rarely white flowers. The first photo was taken by Rachel Saunders January 2007 at Silvermine where it was growing in very acidic and nutrient poor soils. The second photo was taken by Cameron McMaster near Napier in the Overberg.
Thereianthus ixioides G.J.Lewis grows on sandstone mountain slopes in the southwestern Cape. The leaves are linear and the flowers white with violet markings in the center. The inflorescence is a dense spike. Photos from Rachel Saunders taken near Franschoek show the beetle pollinators.
Thereianthus minutus (Klatt) G.J.Lewis grows in seeps and wet sandstone rocks in the Western Cape. Plants grow 10 to 20 cm high. Leaves are sword-shaped to falcate with a midrib and flowers are bright pinkish purple. The first three photos were taken by Andrew Harvie near Bainskloof. The last photo was taken by Bernhard Frauenknecht in mid December 2023.
Thereianthus spicatus (L.) G.J.Lewis is found on sandstone slopes in the southwestern Cape. It blooms in spring, especially after fire. Growing 20 to 30 cm high, it has pale blue to mauve flowers in a dense spike with darker markings on the lower tepals. The first four photos from iNaturalist were taken by Carina Lochner in November in the Western Cape and shared under a CC BY-NC license. The last photo was taken by Rod Saunders.