Thursday 2 May 2024

Casearia septandra: A new species of tree from southern Guinea.

The genus Casearia comprises fruiting trees in the Willow Family, Salicaceae, found throughout the tropics. There are currently three described species known from West Africa, Casearia inaequalis from Sierra Leone and Côte d'Ivoire, Casearia prismatocarpa, which is found from Sierra Leone, Guinea, and Liberia south to the Congo Basin, and Casearia gambiana, currently known only from The Gambia.

In a paper published in the journal Kew Bulletin on 13 April 2024, Frans Breteler, formerly of the Herbarium Vadense, and Abdoulaye Baldé of the Centre de Formation de Nzérékoré, describe a new species of Casearia from the mountains of southern Guinea. 

The new species is named Casearia septandra, although no explanation is given for this name. It is a tree-forming species reaching about 20 m in height with a trunk diameter at breast height of about 36 cm. Leaves are oval and reach about 3.5 cm in length, flowers are small and white, fruit are orange and up to 1 cm in diameter, spliting into three valves as they ripen.

Casearia septandra. (A) Leafy branchlet; (B) fruits; (C) dehisced fruit. Abdoulaye Baldé & Xander van der Burgt in Breteler & Baldé (2024).

Casearia septandra grows in montane rainforests at altitudes of greater than 900 m above sealevel, in the mountains of southern Guinea. A total of five specimens were located, growing at three separate locations. In addition, some material in a dried herbarium specimen collected in 1949 is considered to belong to the species, although the collection location details are unclear, making it uncertain if this material came from one of the known localities for the species. 

Distribution of Casearia septandra. Breteler & Baldé (2024).

Given the low number of living specimens and the limited geographical distribution of the species, Breteler and Baldé suggest that Casearia septandra be classified as  Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, although they note that two of the locations at which Casearia septandra was found are threatened by potentialiron ore mining, and that if this goes ahead the species should be reclassified as Critically Endangered. 

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