Solanum phoxocarpum (osigawai)

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

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 (Image: Maria Vorontsova)

Solanum phoxocarpum is a woody shrub or tree measuring 3-6 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. The leaves are 6-8 cm long, dark green above and white-grey underneath. 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. 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. Each berry contains about 30 seeds, 4-4.5 mm long, flat and kidney-shaped.

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 (Image: Maria Vorontsova)

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. 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.

Young shrubby Solanum phoxocarpum with the prominent yellow pointed fruits (Image: Maria Vorontsova)

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)

Cross section through a Solanum phoxocarpum fruit with brown seeds visible inside (Image: Maria Vorontsova)

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.

Collecting fruits of Solanum phoxocarpum in the Aberdare Mountains, Kenya (Image: Maria Vorontsova)

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. 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.

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.

The discovery of Solanum phoxocarpum was sponsored by the PBI Solanaceae Source project , aiming to publish information on all 1,500 species of Solanum (funded by the National Science Foundation, USA).

Maria Vorontsova was employed at the Natural History Museum, London when this work was carried out.

Tanzania 2010 fieldwork blog by Kew botanist Maria Vorontsova: Hunt for wild spiny aubergines.