Zurich Herbarium (Z+ZT) - Sebaea

Sebaea welwitschii? Yes and no!

ZT-00079984 - United Herbaria Z+ZT - CC BY 4.0

Among the many species Hans Hess harvested during his 1951-52 expedition to Angola, there are perfectly preserved specimens of a majestic gentian with large salmon corollas. Hess himself identified it as a "Sebaea welwitschii Schinz", as evidenced by the handwritten inscription on the label.

If we accept the conclusion of Hess, we have in front of us a gentian described by the Zurich botanist Hans Schinz, in 1891, and named in honor of Friedrich Welwitsch. The latter was both a physician and director of the botanical garden of Lisbon, an institution he greatly enriched with collections from his seven-year trip to Angola (1853-1860). Welwitsch himself became famous for the "fossil" genus Welwitschia, named in his honor by Joseph Dalton Hooker in 1863.

Over time, the combination of Schinz proved to be superfluous. Indeed, an identical species had already been described in 1846, under the name Cicendia microphylla Edgew, and was later transferred into the genus Sebaea by Emil Knoblauch. The firstborn being always right – at least under the laws of botanical nomenclature - the combination dedicated to Welwitsch should be considered a synonym (a "heterobasionym" in the specialized jargon) and the Sebaea welwitschii Schinz of Hess renamed S. microphylla (Edgew) Knobl.

At this point, the epithet "microphylla" somehow attracted my attention, given the vigorous aspect of the organs in question on the given sample! I, therefore, decided to consult the holotype of this so-called Sebaea microphylla – and by the same occasion that of S. welwitschii – in order to overcome a possible error of identification... Ty surprise, this control revealed a plant with Lilliputian leaves and similarly small flowers. In other words… nothing that matches the actual voucher. A taxonomic revision appears necessary!

The paucity of the number of species of Sebaea sensu-lato in Angola (13 species for 33 Gentianaceae(1)), as well as the size and color of the corollas, allows to reduce the list of candidates to only two species: S. grandis (Mey.) Steud. and S. primulaeflora (Welw.) Sileshi. The latter species differs from the former by the basal branching of the stems and a maximum size of 15 cm, much resembling the species collected by Hess, on May 17, 1952!

To complete our diagnosis, we must finally take into account the fact that the genus Sebaea was recently dismembered into four natural entities on the basis of molecular data (2), Sebaea primulaeflora (Welw.) Sileshi becoming (or rather reversing to) Exochaenium primulaeflorum Welw., a combination already proposed by… Welwitsch in 1869!

Finally, Hess was not completely wrong when he associated his sample with Welwitsch's name!

Guilhem Mansion

Bibliographie

1. Figueiredo E and Smith GF. 2008. Plants of Angola. Strelitzia 22. South African National Biodiversity Institute, Pretoria.

2. Kissling J, Yuan YM, Küpfer P, and Mansion G. 2009. The polyphyletic genus Sebaea (Gentianaceae): A step forward in understanding the morphological and karyological evolution of the Exaceae. Molecular Phylogenetics and Evolution 53: 734-748.