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Plant story - Polhillia obsoleta, an endangered shrub from South Africa

With the common name Teesuikerkaroo bos, Polhillia obsoleta is an endangered shrub from the Western Cape Province of South Africa.

Polhillia obsoleta - Common name: Teesuikerkaroo bos

Finding Polhillia obsoleta

Polhillia obsoleta has the status of Endangered on the IUCN Red List for South Africa and with this in mind the Millennium Seed Bank Partnership targeted this plant species for collection into the bank. All three Renosterveld species were hard to find but the Polhillia was the most difficult. It took Olivia Pekeur of the Cape team, two flowering seasons to find and identify the correct specimen and then time the collection of seed correctly. Finally though, the last two known populations were located and on 1 November 2007 ripe healthy seed was collected.

The municipality of Worcester have been made aware of the value of these populations and are acting to save the land that they grown on from development.

This small erect, many-branched shrub grows up to 1.5 m high. The linear leaves are silky and are bright reflective silver in the summer sunshine. It has pale yellow flowers that are found at the tips of the branches and are rather insignificant. It is the seed pods that are the most attractive feature of this plant; they are 2-3 cm long and pleated, giving the plant a shaggy look in the open veld. The pods are covered with smooth silver hairs and are velvety to the touch. Polhillia flowers in the early spring (July-September) in South Africa and the seeds are released in late autumn before the rainy season. There are seven species in this genus, which is endemic to the Western Cape Province of South Africa.

Polhillia obsoleta occurs in the Renosterveld vegetation type, one of South Africa’s (and the worlds) most endangered vegetation types, with little more than 5% remaining intact. Polhillia obsoleta grows in Central Mountain Renosterveld, an area of 7,611 km², of which approximately 11% is transformed and only 3.63% conserved.

A vital element of the local ecosystem

Renosterveld vegetation occurs in fertile soils that are not leached of their minerals like Fynbos soils. Polhillia obsoleta, a legume, plays a vital role in the ecosystem in which it grows. It is threatened, however, due to this high fertility, and most of the area has been converted to agriculture. It is increasingly being cultivated for cereals, propagation of vegetable seed and used as augmented pasture. Where sufficient water is available it is being extensively cleared for fruit orchards. This vegetation type is also used for grazing and ostrich farming, which is prevalent in the Little Karoo area.

Due to the high fertility of the soil, it is probable that herds of large game once occurred in Renosterveld. Mountain zebra, quagga, bluebuck, red hartebeest, eland, bontebok, elephant, black rhino and buffalo were common, as well as the big cats, lion, cheetah, and leopard. Of these only the mountain zebra and leopard have survived in the Central Mountain Renosterveld (by retreating to the mountains). All the other species became extinct in this vegetation type and the quagga and bluebuck are completely extinct. It is now becoming increasingly possible that plants like Polhillia obsoleta (teesuikerkaroo bos / teasugarkaroo bush), Leucadendron flexuosum (Worcester cone bush) and Leucadendron chamaelea (Witsenberg cone bush) will join the quagga and bluebuck’s fate in the Renosterveld if little, or nothing, is done now to prevent the loss of the remaining natural veld.

Name: Polhillia obsoleta (Harv.) B.-E.van Wyk (= Polhillia waltersii (C.H.Stirt.) C.H.Stirt.)
Family: Leguminosae – subfam. Papilionoideae – tribe Crotalarieae

By Carly Cowell, SANBI, Kirstenbosch National Botanic Garden, Cape Town, Republic of South Africa

Picture by Caitlin von Witt, CREW project

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