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Solanum phoxocarpum (osigawai)

Solanum phoxocarpum is a spiny African tree with bright yellow pointed fruits that may have medicinal properties.

Branch of Solanum phoxocarpum with unusual pointed fruits and almost no lobes on the leaves

Branch of Solanum phoxocarpum, with unusual pointed fruits and almost no lobes on the leaves, in the Aberdare Mountains, Kenya. Nobody knows what kinds of animals eat these fruits.

Species information

Scientific name: 

Solanum phoxocarpum Voronts.

Common name: 

osigawai, sigawet (Masai language, Kenya)

Conservation status: 

Not yet assessed according to IUCN criteria.

Habitat: 

Open montane woodlands.

Key Uses: 

Medicinal, hedging, possibly edible.

Known hazards: 

It seems that the fruits could be poisonous – in 2009 a staff member on the Kenya ‘Seeds for Life’ project was preparing seeds for storage and became unwell after inhaling the vapours from cut fruits.

Taxonomy

Subclass: 
Superorder: 
Asteranae
Order: 
Solanalaes
Family: 
Solanaceae
Genus: Solanum

About this species

One of the wild spiny aubergine species of Africa, Solanum phoxocarpum is a shrub or small tree that grows at high altitudes in Kenyan and Tanzanian mountains. It can grow up to six metres tall, and has unusual long, yellow, pointed fruits and mauve flowers. It was recognised as a new species by Kew botanist Dr Maria Vorontsova during fieldwork in Kenya’s Aberdare Mountains in April 2009.

Genus: 
Solanum

Discover more

Geography and distribution

Native to Kenya and Tanzania, Solanum phoxocarpum lives in open montane woodlands at 2,100 - 3,000 metres above sea level.

Description

Long-styled flower of Solanum phoxocarpum. There is an opening at the tip of each anther and when bees land on the anthers and 'buzz', pollen shoots out. Long-styled flowers produce fruits if they are fertilised by the bees.

Overview: Solanum phoxocarpum is a woody shrub or tree measuring 3 to 6 m tall, with several stems growing out of the ground. It is covered in numerous star-shaped hairs barely visible to the naked eye, each hair being around 0.5 mm wide with 11-16 side rays. The main stems bear large curved prickles measuring 0.6-1.5 cm long. Botanically, these are called prickles rather than spines because the structures arise from the epidermis rather than from inner vascular bundles.

Leaves: The leaves are 6-8 cm long, dark green above and white-grey underneath.

Flowers: There are 1-7 flowers in every inflorescence. The lowermost flower is larger than the others, 3 cm in diameter when fully open, and when fertilised can develop into a fruit. The other flowers are 1.7 cm in diameter and produce functional pollen but cannot produce fruit. The petals are pale purple and the anthers are 3.5-4 mm long, with openings at the tips.

Fruits: The fruit is a berry with an unusual conical shape, apically pointed and retaining the same elongated pointed shape throughout development. There is usually one fruit of 2.8-3.7cm long per fruit-bearing branch. The surface of the fruit is usually smooth and shiny but sometimes has small warts. The fruits are yellow when ripe, held erect on the pedicels while they ripen, and start to hang downwards when mature.

Seeds: Each berry contains about 30 seeds, 4-4.5 mm long, flat and kidney-shaped.

Threats and conservation

Solanum phoxocarpum should not be in danger of extinction because its habitat is protected by a network of National Parks in Kenya and Tanzania, including the Aberdare National Park (Kenya), Mount Kenya National Park (Kenya) and the Ngorongoro Conservation Area (Tanzania).

In spite of the protection offered by these National Parks, populations of S. phoxocarpum are decreasing both inside and outside of protected areas due to the clearing of land for cultivation. 

Plant hunting team in the Aberdare Mountains, Kenya, collecting fruits of Solanum phoxocarpum. All scientists in the National Park must be accompanied by an armed park ranger because of populations of dangerous elephants.

During an expedition in April 2009 scientists visited areas where this species had been recorded during the twentieth century, and in place of many forests there are now only villages and fields. Human activities such as cultivation and village-building have expanded in the areas surrounding the National Parks and pose potential threats to this species.

Uses

The following uses have been documented by plant collectors on herbarium specimen labels, though have not yet been verified in the field:

  • The plants can be used for hedges (Kenya, recorded in 1939)
  • The fruit is eaten (Kenya, recorded in 1965)
  • Roots are boiled in water and the liquid mixed with a broth and taken as a remedy for gonorrhoea. The ripe dry fruits can also be roasted and then ground to a powder, and mixed with butter to give to babies (although the purpose of this has not been recorded) (Kenya, recorded in 1961)

Millennium Seed Bank: Seed storage

Cross section through a Solanum phoxocarpum fruit with brown seeds visible inside.

Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

Description of seeds: 4-4.5 mm long, flat and kidney-shaped
Number of seed collections stored in the Millennium Seed Bank: One
Germination testing: 100 % germination was achieved on a germination medium of 1% agar at a temperature of 25°C, with 8 hours of daylight followed by 16 hours of darkness.

Collaboration leads to discovery

The discovery of this species was made possible by Tim Pearce of Kew’s Millennium Seed Bank Partnership in collaboration with the Kenya ‘Seeds for Life’ project, the National Museums of Kenya, Patrick Muthoka, and Paul Kirka. 

Collecting fruits of Solanum phoxocarpum in the Aberdare Mountains, Kenya.

During collaborative fieldwork in the Kenyan Aberdare mountains in 2009, seeds of Solanum phoxocarpum were collected for seed-banking at the same time as the distinctness of this species was firmly established by Kew botanist Dr Maria Vorontsova.

This species at Kew

There are 17 preserved specimens of Solanum phoxocarpum held in Kew’s behind-the-scenes Herbarium. It was these collections that prompted the recognition of S. phoxocarpum as a new species and the expedition to find living specimens in Kenya.

References and credits

Edmonds, J.E., Vorontsova, M.S. & Knapp, S. Solanaceae. In: Flora of Tropical East Africa, ed. H. Beentje, Royal Botanic Gardens, Kew. In preparation. 

Lambrechts, C., Woodley, B., Church, C. & Gachanja, M. (2003). Report on the Aerial Survey of the Destruction of the Aberdare Range Forests. United Nations Environment Programme, Nairobi.

PBI Solanum Project (2010). Solanaceae Source. Available online (accessed 25 November 2010). 

Vorontsova, M.S., Christenhusz, M.J.M., Kirika, P. & Muthoka, P. (2010). Three new species of Solanum from Kenya: using herbarium specimens to document environmental change. Systematic Botany 35: 894-906.

Kew Science Editor: Maria Vorontsova
Kew contributors: Tim Pearce (Millennium Seed Bank)
Copyediting: Emma Tredwell
Kew would like to thank the following contributors: Dr Sandy Knapp (Natural History Museum and the PBI Solanum Project), Dr Maarten Christenhusz (Natural History Museum), Dr Geoffrey Mwachala, Nicholas Cheva, Jonathan Ogweno (National Museums of Kenya), Dr Patrick Muthoka and Paul Kirika (National Museums of Kenya and the Seeds for Life Project), Kenyan Wildlife Service, British Airways for sponsoring expedition flights.

While every effort has been taken to ensure that the information contained in these pages is reliable and complete, the notes on hazards, edibility and suchlike included here are recorded information and do not constitute recommendations. No responsibility will be taken for readers’ own actions.

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