Stokoe’s bush iris (Nivenia stokoei)

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Nivenia stokoei flowering plant
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Stokoe’s bush iris fact file

Stokoe’s bush iris description

KingdomPlantae
PhylumTracheophyta
ClassMagnoliopsida
OrderLiliales
FamilyIridaceae
GenusNivenia (1)

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).

Size
Height: up to 60 cm (2)
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Stokoe’s bush iris biology

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).

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Stokoe’s bush iris range

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

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Stokoe’s bush iris habitat

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

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Stokoe’s bush iris status

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

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Stokoe’s bush iris threats

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.

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Stokoe’s bush iris conservation

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).

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Find out more

For further information on Stokoe’s bush iris see:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
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Glossary

Cape Floristic Region
An area occupying about 90,000 square kilometres in South Africa that contains an incredibly high diversity of plant species (around 8,700 species), of which 68 percent are found no where else.
Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Fynbos
The natural shrubland vegetation occurring in the southwestern and southern Cape of South Africa, holding the greatest diversity of plant species in the world. Fynbos is characterised by tall shrubs with large leaves, heath-like shrubs, wiry reed-like plants, and bulbous herbs.
Heterostyly
A heterostylous plant produces two or more types of flowers, each with stamens and styles of different lengths.
Pollination
The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
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References

  1. PlantZAfrica (February, 2008)
    http://www.plantzafrica.com/plantnop/niveniastokei.htm
  2. Goldblatt, P. and Manning, J. (2000) Cape Plants: A Conspectus of the Cape Flora of South Africa. National Botanical Institute of South Africa, Pretoria .
  3. Threatened Species Programme. (2007) Interim Red Data List of South African Plant Taxa. South African National Biodiversity Institute, Pretoria, South Africa. Available at:
    http://www.sanbi.org/biodiversity/reddata.htm
  4. Paterson-Jones, C. and Manning, J. (2007) Ecoguide Fynbos. Briza Publications, Pretoria, South Africa.
  5. Ornduff, R. (1983) Studies on the reproductive system of Nivenia corymbosa (Iridaceae), an apparently androdioecious species. Annals of the Missouri Botanical Garden, 70(1): 146 - 148.
  6. Mulcahy, D.L. (1965) Heterostyly within Nivenia (Iridaceae). Brittonia, 17: 349 - 351.
  7. Allaby, M. (1998) Dictionary of Plant Sciences. Oxford University Press, Oxford.
  8. UNESCO Biosphere Reserves (February, 2008)
    http://www.unesco.org/mab/BRs.shtml
  9. UNEP-WCMC: Cape Floral Protected Areas of South Africa (February, 2008)
    http://www.unep-wcmc.org/sites/wh/pdf/CAPE%20FLORAL%20REGION.pdf
  10. Carolus, B. (2004) Living Plant Collections: Threatened Plants Programme. SABONET News, 9(1): 37 - .
  11. Pienaar, K. (2003) South African ‘What Flower is That’?. Struik Publishers, Cape Town.
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Image credit

Nivenia stokoei flowering plant  
Nivenia stokoei flowering plant

© Dr Paul Godard

Paul Godard - Soul Photography
Cape Town
South Africa
arkive@wildscreen.org.uk
http://www.paulgodard.com/

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