Sunday 15 February 2015

Two new species of Oxalis from Northern Cape Province, South Africa.

Plants of the genus Oxalis are found in South America, where there are around 250 species of herbs, shrubs and vines, and Southern Africa, where there are around 210 species, all of which are bulbous perennials, and most found within the Cape Floristic Province. Classification of the South African species has proved difficult, as many species are highly variable, making identification difficult. Recent application of genetic barcoding to the group suggests that South African members of the group can be split into three clades (a clade is a group of organisms with a shared common ancestor; all members of the clade must descend from that ancestor and everything shown to be descended from that ancestor must be included in the clade). One of these, the Oxalis pes-caprae clade, apparently containing the majority of species found outside the Cape Floristic Province, in Northern Cape Province and Namibia.

In a paper published in the journal Blumea on 17 November 2014, Francois Roets of the Department of Conservation Ecology and Entomology at Stellenbosch University, Kenneth Oberlander of the Department of Conservation Ecology and Entomology at Stellenbosch University and the Institute of Botany at the Academy of Sciences of the Czech Republic and Leanne Dreyer of the Department of Botany and Zoology at Stellenbosch University, describe two new species of Oxalis from Northern Cape Province, both of which are placed in the Oxalis pes-caprae clade.

The first new species is named Oxalis hirsutibulba, meaning ‘hairy-bulbed’ in reference to the dense hairs on the bulbs and rhizomes of this species. This is a bright green plant reaching 20 cm tall covered by dense, fine hairs, and growing in rocky environments. Bulbs reach 6 cm in length and are and shallowly buried, rhizomes reach 20 cm. Three to fourteen trifoliate leaves are produced, and one to seven tube shaped white flowers with yellow interiors.

Flowers of Oxalis hirsutibulba. Roets et al. (2014).

Oxalis hirsutibulba was found growing at three locations in the Richtersveld Conservancy UNESCO World Heritage Site. It was collected from two south facing slopes by Roets et al., one with desert vegetation and one with succulent Karoo vegetation. Some previously collected herbarium specimens were also found to belong to the species; these were identified as having come from Helskloof Pass near Kubas, but the exact location of their origin is unknown.

Typical habitat of Oxalis hirsutibulba in the Richtersveld Conservancy. Roets et al. (2014).

The second new species is named Oxalis fenestrata, meaning ‘having windows’, which is not explained but which probably refers to the translucent white markings just below the apical incision of the leaflets. This species has thick, succulent stems reaching 40 cm tall, and is a bright apple green colour. The bulbs reach 7.5 cm long and are buried up to 30 cm deep, the rhizome is white and reaches 25 cm. Leaves are trifoliate and found in groups of three to five. One to six flowers are produced, each having yellow funnel-shaped tube surrounded by five white petals.

(b) Whole plant of Oxalis fenestrata. (d) Detail of leaves. Roets et al. (2014).

Oxalis fenestrata was found growing on granite boulder-dominated hillsides in the southern part of the Richtersveld Conservancy; only two populations were found, separated by a distance of 1.3 km, suggesting the species has a limited geographical range. All the planets were found growing in gravel, in the shade of large boulders or Fig trees. Neither population comprised more than 50 individuals.

Typical habitat of Oxalis fenestrata in the Richtersveld Conservancy. Roets et al. (2014).

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