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Taxonomy of Atlantic Central African orchids 2. A second species of the rare genus Distylodon (Orchidaceae, Angraecinae) collected in Cameroon.

ABSTRACT: While conducting field inventories in South Cameroon, we collected two specimens of a new species that we considered to belong to the genus Angraecopsis. Afterwards, a careful examination of specimens housed at main herbaria, along with the nomenclatural types, allows us to place it in Distylodon, a monotypic genus previously known from East Africa. Distylodon sonkeanum Droissart, Stévart & P.J.Cribb, sp. nov. was collected in the lowland coastal forest of Atlantic Central Africa. It is known from a single locality in the surroundings of the Campo-Ma'an National Park. The species differs from D. comptum, by its several-flowered inflorescences, longer leaves and spur, and shorter pedicel and ovary. The species appears to be rare and is assessed as Critically Endangered [CR B2ab(iii)] according to IUCN Red List Categories and Criteria. New field investigations are required to attempt to find it in the low-elevation parts of the Campo-Ma'an National Park in Cameroon.

SUBMITTER: Droissart V

PROVIDER: S-EPMC4023340 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Taxonomy of Atlantic Central African orchids 2. A second species of the rare genus Distylodon (Orchidaceae, Angraecinae) collected in Cameroon.

Droissart Vincent V Cribb Phillip J PJ Simo-Droissart Murielle M Stévart Tariq T

PhytoKeys 20140409 36

While conducting field inventories in South Cameroon, we collected two specimens of a new species that we considered to belong to the genus Angraecopsis. Afterwards, a careful examination of specimens housed at main herbaria, along with the nomenclatural types, allows us to place it in Distylodon, a monotypic genus previously known from East Africa. Distylodon sonkeanum Droissart, Stévart & P.J.Cribb, sp. nov. was collected in the lowland coastal forest of Atlantic Central Africa. It is known fr ...[more]

PMID: 24843291

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Project description:BackgroundThe temporal origin and diversification of orchids (family Orchidaceae) has been subject to intense debate in the last decade. The description of the first reliable fossil in 2007 enabled a direct calibration of the orchid phylogeny, but little attention has been paid to the potential influence of dating methodology in obtaining reliable age estimates. Moreover, two new orchid fossils described in 2009 have not yet been incorporated in a molecular dating analysis. Here we compare the ages of major orchid clades estimated under two widely used methods, a Bayesian relaxed clock implemented in BEAST and Penalized Likelihood implemented in r8s. We then perform a new family-level analysis by integrating all 3 available fossils and using BEAST. To evaluate how the newly estimated ages may influence the evolutionary interpretation of a species-level phylogeny, we assess divergence times for the South American genus Hoffmannseggella (subfam. Epidendroideae), for which we present an almost complete phylogeny (40 out of 41 species sampled).ResultsOur results provide additional support that all extant orchids shared a most recent common ancestor in the Late Cretaceous (approximately 77 million years ago, Ma). However, we estimate the crown age of the five orchid subfamilies to be generally (approximately1-8 Ma) younger than previously calculated under the Penalized Likelihood algorithm and using a single internal fossil calibration. The crown age of Hoffmannseggella is estimated here at approximately 11 Ma, some 3 Ma more recently than estimated under Penalized Likelihood.ConclusionsContrary to recent suggestions that orchid diversification began in a period of global warming, our results place the onset of diversification of the largest orchid subfamilies (Orchidoideae and Epidendroideae) in a period of global cooling subsequent to the Early Eocene Climatic Optimum. The diversification of Hoffmannseggella appears even more correlated to late Tertiary climatic fluctuations than previously suggested. With the incorporation of new fossils in the orchid phylogeny and the use of a method that is arguably more adequate given the present data, our results represent the most up-to-date estimate of divergence times in orchids.

Project description:The Vanilloideae (vanilloids) is one of five subfamilies of Orchidaceae and is composed of fourteen genera and approximately 245 species. In this study, the six new chloroplast genomes (plastomes) of vanilloids (two Lecanorchis, two Pogonia, and two Vanilla species) were decoded, and then the evolutionary patterns of plastomes were compared to all available vanilloid plastomes. Pogonia japonica has the longest plastome, with 158,200 bp in genome size. In contrast, Lecanorchis japonica has the shortest plastome with 70,498 bp in genome size. The vanilloid plastomes have regular quadripartite structures, but the small single copy (SSC) region was drastically reduced. Two different tribes of Vanilloideae (Pogonieae and Vanilleae) showed different levels of SSC reductions. In addition, various gene losses were observed among the vanilloid plastomes. The photosynthetic vanilloids (Pogonia and Vanilla) showed signs of stage 1 degradation and had lost most of their ndh genes. The other three species (one Cyrotsia and two Lecanorchis), however, had stage 3 or stage 4 degradation and had lost almost all the genes in their plastomes, except for some housekeeping genes. The Vanilloideae were located between the Apostasioideae and Cypripedioideae in the maximum likelihood tree. A total of ten rearrangements were found among ten Vanilloideae plastomes when compared to the basal Apostasioideae plastomes. The four sub-regions of the single copy (SC) region shifted into an inverted repeat (IR) region, and the other four sub-regions of the IR region shifted into the SC regions. Both the synonymous (dS) and nonsynonymous (dN) substitution rates of IR in-cooperated SC sub-regions were decelerated, while the substitution rates of SC in-cooperated IR sub-regions were accelerated. A total of 20 protein-coding genes remained in mycoheterotrophic vanilloids. Almost all these protein genes show accelerated base substitution rates compared to the photosynthetic vanilloids. Two of the twenty genes in the mycoheterotrophic species faced strong "relaxed selection" pressure (p-value < 0.05).

Dataset Information

Taxonomy of Atlantic Central African orchids 2. A second species of the rare genus Distylodon (Orchidaceae, Angraecinae) collected in Cameroon.

Publications

Taxonomy of Atlantic Central African orchids 2. A second species of the rare genus Distylodon (Orchidaceae, Angraecinae) collected in Cameroon.

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