Solanum ruvu

The area where Solanum ruvu used to grow is now cultivated to grow bananas, papaya, manihot, and rice (Image: Maria Vorontsova)

Known from only a single collection in the Ruvu Forest in the Morogoro District of Tanzania.

Coastal forests were once widespread along the eastern African seaboard but the majority have now disappeared leaving over 250 known remnant forest patches. These patches are typically isolated from each other by a mixture of farmland and thicket areas. Many have exceptional levels of local endemism, but are small, fragmented, surrounded by populated areas and are becoming rapidly degraded. The Ruvu Catchment Forest Reserve is poorly known and has not been explored in detail by botanists. It is situated in the eastern foothills of the Uluguru mountains and managed by the Forest Catchment project of the Morogoro Region. Solanum ruvu is known from a single collection made by the Frontier-Tanzania Coastal Forest Research Programme in 2000, most likely in the part of Ruvu Forest now known as the Chafungo forest fragment.

Solanum ruvu herbarium specimen collected by B. Mhoro and the Frontier-Tanzania Programme in the Ruvu Forest Reserve (Image: RBG Kew)

Solanum ruvu is a climbing herb or shrub with a dense covering of 4-6 mm long straight prickles. The leaves are 9-12 x 2.5-4.5 cm and are very thin, with almost no hairs. The unbranched inflorescences are 5-9 cm long, and bear 10-15 flowers. The inflorescence stalk is densely prickly. Only one or two flowers are open at any one time. The flowers are 1.2-1.8 cm wide, with long thin petals of 6-8 × 1.5-2 mm. The anthers are 5-6 mm long, and have openings at the tips.

The only information we have about this species comes from a single herbarium collection (two herbarium specimens) and hence other details such as plant height, flower colour, fruits and seeds are unknown.

Botanical drawing of Solanum ruvu showing the habit and enlarged prickles, flowers, and tiny star-shaped hairs (Drawn by Lucy T. Smith ©)

The Chafungo forest fragment is a highly fertile area with black cotton soil over limestone, and is difficult to reach by road. The Waluguru people were moved to the area during agricultural reforms in 1974 and population growth as well as clearance of the natural vegetation for agriculture has been on the increase ever since. The usual sequence of land cultivation starts with planting maize for the first two seasons following forest-clearance, later followed by matrix crops, including bananas, rice, sesame, tomato, and manihot (cassava). Sesame is also grown as a cash crop and provides the highest profit. Trees in the Chafungo forest fragment are said to have been cleared in 2003. Currently, the majority of the land there is used to grow rice and sesame. Approximately 3% of the area is occupied by limestone rocks and cannot be cultivated. Forest fragments with remnant natural vegetation can still be found on these limestone outcrops.

The membranous leaves of Solanum ruvu, which almost completely lack indumentum (a covering of fine hairs or bristles), suggest that the species inhabited the dark and wet forest understorey, making it unlikely to survive clearance for agriculture. The Chafungo thicket vegetation, the nearby Kingira and Loholole fragments, and the surrounding area, were thoroughly searched during an expedition to Tanzania in March 2010. In none of the nearby forest fragments was a full tree canopy preserved, and S. ruvu was not refound. Local people did not recognise pictures of the plant and there is a real probability that this species may already have been driven to extinction. 

The only wild vegetation remaining in the Ruvu forest is restricted to the white limestone boulders where cultivation is not possible. Rice is seen growing in the foreground (Image: Maria Vorontsova)

An international botanical expedition, involving Maria Vorontsova (whilst working for the Natural History Museum, London and collaborating with Kew), Eric Tepe (University of Utah) and Frank Mbago (University of Dar es Salaam) searched for Solanum ruvu in March 2010. Searches were carried out in the Ruvu Forest and the Chafungo forest fragment at the exact latitude and longitude specified by the original collection. After two days of searching it was concluded that no intact coastal forest remained anywhere near the original collection area and that the forest fragments were not large enough to provide a forest canopy to support an understorey species such as S. ruvu.

There are only two known herbarium specimens of this species: one held at Kew’s behind-the-scenes Herbarium, and one at the Missouri Botanical Garden, USA.

The discovery of Solanum ruvu was sponsored by the PBI Solanaceae Source project, which publishes information on all 1,500 species of Solanum (grant funding from NSF)

Maria Vorontsova was employed on the PBI Solanum project based at the Natural History Museum, London.

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