Stokoe’s bush iris  (Nivenia stokoei)

Classified as Least Concern (LC) on the Interim Red Data List of South African Plant Taxa (3).

Stokoe’s bush iris is an evergreen shrub, noted for its clusters of striking blue flowers (4). The sword-shaped leaves, measuring 8 to 13 centimetres long and up to five millimetres wide, are arranged like a fan (1). The woody stem, which has a hard, brittle texture, grows from a thickened, underground, fire-resistant base (1). When in bloom, clusters of 20 to 40 flowers are borne at the end of the stems. These large flowers, in various shades of blue, have a slender tube at the base, measuring 40 to 50 millimetres long (4).

Endemic to the Kogelberg Biosphere Reserve in the Western Cape Province of South Africa (1).

Stokoe’s bush iris grows in rocky sandstone, at the foot of mountains in fynbos (2)

Like all Nivenia species, Stokoe’s bush iris is interesting because it is one of the few plants in the iris family that exhibits heterostyly. Nivenia species produce two different types of flowers; one has a long style and short stamens, the other has long stamens and a short style (5) (6). This prevents the anthers and stigmas in each flower from coming into contact with each other, and prevents self-pollination. The different lengths of stamens and styles are adapted for pollination by different pollinating insects, or different body parts of the same insect. This encourages pollination between the two different flower forms. Cross-pollination ensures the offspring are genetically unique from the parents and thus maintains genetic diversity; an advantage in a changing environment (7).

The stunning flowers of Stokoe’s bush iris, which bloom from February to March (2), are pollinated by visiting insects, including flies of the family Nemestriniidae and long-tongued bees belonging to the family Anthophorideae (1).

Stokoe’s bush iris has been classified as Least Concern, but is rare, meaning that while this species is not currently threatened, its very small distribution makes it a species of conservation concern (3). Species with restricted ranges or small populations are particularly vulnerable to the impacts of any threatening event, which could rapidly affect every individual in the population.

This rare iris species is found only within the Kogelberg Biosphere Reserve (1), an area which promotes reconciling the conservation of biodiversity with its sustainable use (8). Kogelberg Biosphere Reserve occurs within the Cape Floristic Region, a unique area valued for its incredible diversity in plants, most of which are found no where else in the world (9). Stokoe’s bush iris was selected as a flagship species for a Threatened Plant Project in Harold Porter National Botanical Garden, and is being cultivated for sale, display and educational purposes (10). Importantly, this is one of only two species of Nivenia that has been cultivated, since the natural conditions of their mountain habitat are not easy to reproduce (11).

For further information on Stokoe’s bush iris see:

• PlantZAfrica:
  www.plantzafrica.com