Thursday, May 3, 2018

[Botany • 2018] Calyptrochilum aurantiacum • New Taxonomic and Conservation Status of Ossiculum (Vandeae, Orchidaceae), A Highly Threatened and Narrow-endemic Angraecoid Orchid from Central Africa

Calyptrochilum aurantiacum 
(P.J.Cribb & Laan) Stévart, M.Simo & Droissart
in Simo-Droissart, Stévart, Sonké, et al., 2018.

photo: V. Droissart 

In the context of producing a revised phylogenetic Linnean taxonomy of angraecoid orchids, the monotypic and narrow-endemic genus Ossiculum is synonymised with Calyptrochilum. Accordingly, a new combination in Calyptrochilum is proposed for Ossiculum aurantiacum. The morphological and DNA-based evidence for this transfer is discussed. Moreover, Calyptrochilum aurantiacum is here firstly reported outside Cameroon, with a record from the Republic of the Congo. The Red List conservation status of this species is reassessed and it is to be downgraded from “Critically Endangered” (CR) to “Endangered” (EN), following the recent discovery of additional subpopulations in Cameroon.

Keywords: Angraecoid orchids, Calyptrochilum, ex situ conservation, IUCN Red List Categories and Criteria, Mungo River Forest Reserve, Odzala National Park, Ossiculum aurantiacum

Calyptrochilum aurantiacum (P.J.Cribb & Laan)
Stévart, M.Simo & Droissart, comb. nov.

Basionym: Ossiculum aurantiacum van der Laan & Cribb, 1986: 824.

Figure 3. Ecology and habit of natural populations of Calyptrochilum aurantiacum.
A Flowering individual growing on upper branches of a felled kola tree, along with the angraecoid orchid Diaphananthe plehniana and the fern Microgramma owariensis. B Dense population growing on 1 metre long branches of Duguetia staudtii. C Calyptrochilum aurantiacum and Diaphananthe plehniana growing side by side on Salacia sp. (Celastraceae). Photographs by V. Droissart (June 2017).

Figure 4. Seed banking of Calyptrochilum aurantiacum in Yaoundé (Cameroon). In 2017, an ex situ conservation programme was initiated to support the long term preservation of C. aurantiacum.
 A Due to the small size of the flowers, manual pollination has been performed under a stereomicroscope. B Fruit development and maturation takes place in a shadehouse established in Yaoundé. C Finally, viable seeds have been harvested and conserved in the freezer (-20°C). Before being preserved at low temperature, seed viability is assessed using the tetrazolium test (red colouration of living embryo).
Photographs A and C by V. Droissart, B by Gyslène Kamdem.

Morphological and DNA-based evidence led to the transfer of the narrow-endemic Ossiculum aurantiacum to the widespread genus Calyptrochilum and, thus, recognises the monotypic genus Ossiculum as a junior synonym of Calyptrochilum. Thanks to recent intensive field trips and laboratory work on central African orchids, new localities of Calyptrochilum aurantiacum have been discovered, a situation that contributed to downgrade the IUCN conservation status of the species. Calyptrochilum aurantiacum is currently known from five locations in two countries (Cameroon and Republic of the Congo) and is assessed as Endangered [EN B2ab(iii,v)] according to the IUCN Red List Categories and Criteria. Fieldwork within and around the Odzala National Park is required to evaluate the species habitat and the state of the subpopulation there. In situ studies on reproductive biology would be necessary for greater efficiency in conservation measures.

 Murielle Simo-Droissart, Tariq Stévart, Bonaventure Sonké, Sandrine Mayogo, Narcisse Kamdem and Vincent Droissart. 2018. New Taxonomic and Conservation Status of Ossiculum (Vandeae, Orchidaceae), A Highly Threatened and Narrow-endemic Angraecoid Orchid from Central Africa.  PhytoKeys. 98: 85-97.  DOI: 10.3897/phytokeys.98.23511

Résumé: En vue de produire une classification taxonomique linnéenne des orchidées angraecoïdes, le genre monotypique Ossiculum, longtemps considéré comme endémique du sud-ouest Cameroun, est placé en synonymie de Calyptrochilum. En conséquence, une nouvelle combinaison dans Calyptrochilum est proposée pour Ossiculum aurantiacum. Les données morphologiques et moléculaires qui justifient cette combinaison sont discutées. L’espèce est signalée pour la première fois hors du Cameroun, en République du Congo. Suite à la découverte récente de sous-populations supplémentaires au Cameroun, le statut de conservation de cette espèce est réévalué selon la liste rouge de l'UICN. Bien que toujours menacée, l’espèce Calyptrochilum aurantiacum est transférée de la catégorie “En danger critique” (CR) vers la catégorie “En danger” (EN).