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Oxygyne duncanii. (A) Whole plant, side view; (B) in habitat (penknife for scale); (C) close-up of flower in situ; (D) preserved specimens in ethanol. All photos by Martin Cheek. Full-size DOI: 10.7717/peerj.4828/fig-7
Source publication
Oxygyne Schltr. (Thismiaceae) is a rare and little-known genus of achlorophyllous mycoheterotrophic perennial herbs with one of the most remarkable distributions of all angiosperm plant genera globally, being disjunct between Japan and West–Central Africa. Each species is known only from a single location, and in most cases from a single specimen....
Context in source publication
Context 1
... life the lamellae form a dome over the mouth of the perianth, with a central aperture and three inconspicuous radial anther slits (Fig. 7). It is possible that the filiform extensions of the lamellae with their capitate apices serve to join firmly the edges of the lamellae into a single structure by locking with each other. In the high rainfall habitat in which this and most other species of the genus occur, the dome could serve to prevent raindrops from flooding the ...
Similar publications
Background and aims
This paper reports a further discovery in the context of a long-term botanical survey in the Cross River-Sanaga interval of west-central Africa, focussing on species discovery and conservation.
Methods
Normal practices of herbarium taxonomy have been applied to study the material collected. The relevant collections are stored i...
Citations
... and P. bogneri Cheek & Moxon-Holt (Cheek et al. 2021;Moxon-Holt & Cheek 2021) although there is always the hope that they will be rediscovered. Completion of formal naming of species in Gabon is vital if further extinctions are to be avoided and if Gabon is not to follow its neighbour, Cameroon, which has the highest number of global extinctions in continental tropical Africa (Humphreys et al. 2019) and where new global plant species extinctions continue to be recorded (Cheek et al. 2017;2018b;2018c;Murphy et al. 2023). ...
Keetia gordonii sp. nov. (Rubiaceae - Vanguerieae) a new species of forest liana from the littoral forest of Gabon is formally described and illustrated as the first endemic species of the genus from that country. On current evidence, the species appears to have three locations and is threatened by forest clearance. It is provisionally assessed using the IUCN 2012 standard as Endangered (EN B2a,b(i-iv). The new species is extremely distinctive within the genus, showing several character states previously unrecorded in Keetia. Keetia gordonii is currently unique in its genus for the massively thick, coriaceous leaf blades seen in the fruiting axillary branches (in this respect resembling a Psydrax Gaertn., vs papery or rarely thinly coriaceous in other Keetia species), and also for the globose, smooth pyrenes (vs ovoid, colliculose in other species), in which the lid crest is so vestigial that it is almost imperceptible (vs lid crest conspicuous in other species). The tanniferous seed endosperm shows a new character state for the genus being present in a continuous, solid layer in the outer part of the seed, rather than being in radial bands or diffuse as in other species of the genus. However, there is no doubt that this taxon is best placed in Keetia as opposed to Psydrax due to the disc concealed deep inside the calyx tube (vs exposed), the presence of a pyrene cap (vs none) and the stipules that lack a well-developed keel (vs keel present). Further, the presence of tanniniferous seed endosperm is not recorded in any other genus of the tribe. Keetia gordonii is currently assigned to the K. hispida species group of Guineo-Congolian Africa.
... The extinction of species such as Oxygyne triandra Schltr. (Thismiaceae, Cheek et al. 2018b) and Afrothisia pachyantha Schltr. (Afrothismiaceae, Cheek & Williams 1999;Cheek et al. 2023d) and at least two species of the African genus Inversodicraea , are well known examples, recently joined by species such as Vepris bali Cheek (Rutaceae, Cheek et al. 2018c), Vepris montisbambutensis Onana (Onana and Chevillotte 2015) and Ardisia schlechteri Gilg (Murphy et al. 2023). ...
Keetia nodulosa Cheek, a cloud forest climber nearly endemic to Cameroon, with a single record from Nigeria, is described and illustrated. It is remarkable as the first known species to be recorded with bacterial leaf nodules (BLN) in the genus Keetia, and also, in the tribe Vanguerieae. Other genera in Rubiaceae with BLN are Psychotria (Psychotrieae-Rubioideae), Sericanthe (Coffeeae) and Pavetta (Pavetteae), both Ixoroideae/Dialypetalanthoideae. The BLN in Keetia (Vanguerieae) are illustrated for the first time here. The characteristics and significance of bacterial leaf nodulation in Keetia nodulosa are discussed in the context of rapidly growing knowledge on the subject in flowering plants. Keetia nodulosa is provisionally assessed using the 2012 IUCN standard as Endangered (EN B2ab(iii)). The importance of its conservation, and options for achieving this are discussed in the context of recent extinctions of other plant species in Cameroon. This discovery of a new cloud forest species is discussed in relation to other cloud forest plant species described in the last twenty years which are also distributed over the highlands of the western half of Cameroon.
... (specifically, Thismia, Tiputinia, Haplothismia, and Oxygyne) as a sister group to Taccaceae Dumort., placing them in a separate subclade from Burmanniaceae within the order Dioscoreales. The recognition of Thismiaceae as a distinct family is further supported by recent phylogenomic studies that focus on high-throughput plastid and mitochondrial data (Garrett et al. 2023;Lam et al. 2018;Lin et al. 2022), and are complemented by morphological data (Cheek et al. 2018;Merckx et al. 2006). ...
... It differed from the species of the two genera of Thismiaceae, Oxygyne and Thismia, distributed in East Asia, in having six stamens (vs. three in Oxygyne) and free stamens touching the stigma during anthesis, a trait absent in Thismia (Cheek et al. 2018;Nuraliev et al. 2021;Shepeleva et al. 2020). The characteristic of free stamens touching the stigma is reminiscent of Afrothismia, a genus exclusively found in Africa (Cheek et al. 2023). ...
... In East Asia, two genera Oxygyne and Thismia within Thismiaceae have been known, both of which occur in Japan (Cheek et al. 2018). Upon detailed examination, we concluded that R. kimotsukiensis did not correspond to either Oxygyne or Thismia. ...
The family Thismiaceae, known as “fairy lanterns” for their urn- or bell-shaped flowers with basally fused tepals, consists of non-photosynthetic flowering monocots mainly in tropical regions, extending into subtropical and temperate areas. Here, we propose a new mycoheterotrophic genus, Relictithismia Suetsugu & Tagane (Thismiaceae), with its monotypic species Relictithismia kimotsukiensis Suetsugu, Yas.Nakam. & Tagane from Kimotsuki Mountains in the Osumi Peninsula, Kagoshima Prefecture, Kyushu Island, southern Japan. Relictithismia resembles Haplothismia Airy Shaw in having a cluster of tuberous roots, a feature previously observed only in this genus within the family Thismiaceae. However, it differs in having solitary flowers (vs. 2–6-flowered pseudo-raceme in Haplothismia ), anther thecae largely separated (vs. connate), and the presence of an annulus (vs. absent). Additionally, Relictithismia differs from the geographically overlapping genus Thismia Griff. in its stamen structure and the position of the annulus. In Relictithismia , the stamens lack connectives, and its free filaments arise from the annulus located inside the perianth mouth, while in Thismia , the stamens typically have connate connectives, forming a staminal tube pendulous from the annulus located at the mouth of the floral tube. Our morphological and phylogenetic data indicated that R. kimotsukiensis holds an early-diverging position within the family, situated outside the Old World Thismia clade. This paper offers an extensive description and color photographs of R. kimotsukiensis , complemented by notes on its phylogenetic relationship and evolutionary history.
... In Cameroon, the lowland forest species Inversodicraea bosii Cusset, Oxygyne triandra Schltr., Afrothismia pachyantha Schltr. have been considered extinct for some years Cheek & Williams 1999;Cheek et al. 2018b;Cheek et al. 2019b). Similarly, Pseudohydrosme bogneri Cheek & Moxon-Holt and P. buettneri Engl. ...
We describe Lychnodiscus bali (Sapindaceae) a new species to science, from the Bali Ngemba Forest Reserve of NW Region Cameroon, the last major remnant of cloud forest in the Bamenda Highlands of Cameroon, recently evidenced as a Tropical Important Plant Area (TIPA or IPA). Confined on current evidence to upper submontane forest, the species is threatened by expanding habitat clearance for farms and is assessed as Critically Endangered. A small tree, attaining 3 – 4 m height, it is the first new species to be added to this Guineo-Congolian tree genus in 50 years, the third recorded from Cameroon, and takes the number of species in the genus to eight. It has the highest known altitudinal range (1700 – 1950 m alt.), of any species of the genus.
Previously identified as Lychnodiscus grandifolius , the new species differs in the shorter length of the distal leaflets (12 – 18 cm vs 22 – 39 cm long), in the abaxial surface lacking glands (vs glands flat and conspicuous), tertiary nerves hairy (vs glabrous), flowers at anthesis 8 – 11 mm long (vs 5 – 7 mm long).
Lychnodiscus bali is described, illustrated and its extinction risk assessment as Critically Endangered is presented. We discuss its discovery in the context of other recently discovered and highly threatened or even extinct plant species in the Cameroon Highlands, and the importance of their conservation.
We present an updated key to the identification of the species of the genus,and discuss its classification in the context of recent molecular phylogenomic studies. Previously placed in Cupanieae by Radlkofer, the authors contend that Lychnodiscus should now be placed in the reconstituted Nepheliaeae in the revised 2021 intrafamilial classification of Buerki et al., probably close to the genera Aporrhiza and Laccodiscus . However, until the genus is included in molecular studies this cannot be confirmed and its sister relationship remains speculative.
... V. onanae is a dioecious evergreen tree that grows between 8 and 20 m tall and is not recorded to have ethnomedicinal uses. The species Vepris onanae is the most recent in a series of plants new to science published from the cloud forests of Cameroon, all threatened with extinction (Cheek et al., 2008(Cheek et al., , 2010(Cheek et al., , 2013(Cheek et al., , 2017a(Cheek et al., , 2017b(Cheek et al., , 2018a(Cheek et al., , 2018c(Cheek et al., , 2020a(Cheek et al., , 2020bCheek and Csiba, 2002) including additional new species of Vepris (Cheek et al., 2018b;Onana et al., 2019;Onana and Chevillotte, 2015). With 24 species of Vepris, Cameroon has the highest species diversity for the genus in Africa (Cheek and Luke, 2022). ...
... ;https://doi.org/10.1101https://doi.org/10. /2023 genera to science, are still steadily being made across Africa and Madagascar (Nuraliev et al. 2016;Cheek et al. 2018c;Cheek et al. 2019d;Cheek et al. 2003;Cheek 2004a; Cheek & Traclet 2020). ...
A new species of Gymnosiphon Blume (Burmanniaceae), G.fonensis Cheek is formally described from the Foret Classee de Pic de Fon, Simandou Range, Guinea-Forestiere, Republic of Guinea (Guinea-Conakry) in West Africa. The new species was formerly confused with and resembles G. bekensis Letouzey of central Africa in the broad flat outer tepal lobes, perianth tube >10 mm long, and (sub)sessile flower. It differs e.g. in that the length of the corolla tube, (13-)14-18 mm, exceeds the corolla diameter (10-11 mm) (vs length of the corolla tube (12 mm) < the corolla diameter (12-15 mm)), the anthers inserted c. 4 mm deep in the corolla tube (vs inserted at the corolla mouth) and the rhizome lacks scale-leaves (vs scale leaves present). Gymnosiphon fonensis is the first known species of its genus and family in which secondary pollen presentation has been recorded. The species is known from five sites, all with threats, in a single threat-based location, accordingly it is assessed as Critically Endangered (CR B1ab(iii)) using the IUCN 2012 standard, making it the most threatened species of Gymnosiphon in continental Africa. The new species is illustrated by colour photos and line-drawings and is mapped. An identification key is provided to the ten species of the genus now known from Africa-Madagascar.
... Setting aside this probable artefact here, members of Thismiaceae are therefore inferred to be monophyletic at the current taxon sampling, and are phylogenetically distinct from Burmanniaceae. Our results are consistent with recognizing Burmanniaceae and Thismiaceae as two distinct lineages in the order, conflicting withJonker (1938), Maas et al. (1986), APG (2003), Caddick et al. (2002a, but in agreement withChase et al. (1995),Merckx et al. (2006), Woodward (2007,Merckx and Smets (2014),Cheek et al. (2018),Lam et al. (2016;2018),Shepeleva et al. (2020) andLin et al. (2022). ...
Premise:
Species in Thismiaceae can no longer photosynthesize, and instead obtain carbon from soil fungi. Here we infer Thismiaceae phylogeny using plastid genome data, and also characterize the molecular evolution of this genome.
Methods:
We assembled five Thismiaceae plastid genomes from genome skimming data, adding to previously published data for phylogenomic inference. We investigated plastid-genome structural changes, considering locally colinear blocks (LCBs). We also characterized possible shifts in selection pressure in retained genes by considering changes in ω, the ratio of non-synonymous to synonymous changes.
Key results:
Thismiaceae experienced two major pulses of gene loss around the early diversification of the family, with subsequent scattered gene losses across descendent lineages. In addition to massive size reduction, Thismiaceae plastid genomes experienced occasional inversions, and there likely were two independent losses of the plastid inverted repeat (IR) region. Retained plastid genes remain under generally strong purifying selection (ω << 1), with significant and sporadic weakening or strengthening in several instances. The bifunctional trnE-UUC gene of Thismia huangii likely retains a secondary role in heme biosynthesis, despite a probable loss of functionality in protein translation. Several cis-spliced group IIA introns are retained, despite the loss of the plastid intron maturase, matK.
Conclusions:
We infer that most gene losses in Thismiaceae occurred early and rapidly, following the initial loss of photosynthesis in its stem lineage. As a species-rich, fully mycoheterotrophic lineage, Thismiaceae provides a model system for uncovering the unique and divergent ways in which plastid genomes evolve in heterotrophic plants. This article is protected by copyright. All rights reserved.
... Diagnostic characters for Afrothismia are presented in Table 1 and Figs 1-4, including a comparison with Thismiaceae (Haplothismia, Oxygyne, Thismia, Tiputinia) and Taccaceae (Tacca). Shaw (1952), Caddick et al. (1998), Caddick et al. (2000a, Cheek et al. (2018a), Maas et al. (1998), Nuraliev et al. (2021, Woodward et al. (2007) and this paper (Fig. 3 D-I, J-L); those for Afrothismiaceae from Cheek (2004a;), Cheek et al. (2019, Cheek & Jannerup (2006); Dauby et al. (2008), Franke (2004), Franke et al. (2004), Maas-van de Kamer (2003), Rübsamen (1986), , , Imhof & Sainge (2008), Imhof et al. (2020) and this paper ( Fig. 3 A-C); those for Taccaceae from Caddick et al. (1998), Caddick et al. (2000a, Drenth (1972), Kubitzki (1998), Watson & Dallwitz (1992 onwards Description as for the genus (see below). ...
... In the Cross-Sanaga Interval of Cameroon, the centre of diversity for Afrothismia with half the accepted species, the best documented global species extinction is another fully mycoheterotrophic species, Oxygyne trianda Schltr. (Thismiaceae, Cheek et al. 2018a). Examples of species becoming extinct before they are known to science appear to be on the increase. ...
Afrothismia is a genus of non-photosynthetic mycoheterotrophs from the forests of continental tropical Africa. Multiple phylogenetic inferences using molecular data recover the genus as sister to a clade comprising mycoheterotrophic Thismiaceae and the photosynthetic family Taccaceae, contrary to earlier placements of Afrothismia and Thismiaceae within Burmanniaceae. Morphological support for separating Afrothismia from the rest of Thismiaceae has depended on the zygomorphic flowers of Afrothismia (although some South American species of Thismia are also zygomorphic) and their clusters of root tubers, each with a terminal rootlet. The number of described species of Afrothismia has recently increased substantially, from four to 16, which has provided additional morphological characters that support its distinction from Thismiaceae. Most notably, the ovary in Afrothismia has a single stalked placenta, and circumscissile fruits from which seeds are exserted by placental elevation (in Thismiaceae, in contrast, there are three placentas, a deliquescing fruit lid, and the seeds are not exserted). Afrothismia stamens are inserted in the lower perianth tube where they are attached to the stigma, and individual flowers are subtended by a single large dorsal bract (in Thismiaceae, stamens are inserted at the mouth of the tube, free of and distant from the stigma, and each flower is subtended by a loose whorl of (2-)3(-4) bracts). Here we formally characterise Afrothismiaceae and review what is known of its development, seed germination, interactions with mycorrhizal Glomeromycota, biogeography, phylogeny and pollination biology. All but one (Afrothismia insignis; Vulnerable) of the 13 species assessed on the IUCN Red List of Threatened Species are either Endangered or Critically Endangered; one species (A. pachyantha Schltr.) is considered to be extinct.
... Until species are described and known to science, it is difficult to assess them for their IUCN conservation status and so the possibility of protecting them is reduced (Cheek et al., 2020). Documented extinctions of plant species are increasing, e.g., in coastal forest of Cameroon, Oxygyne triandra Schltr. is considered extinct at its sole locality, the forest at Mabeta-Moliwe in the foothills of Mt Cameroon (Cheek et al., 2018b;Cheek & Williams, 1999;Cheek, 1992), Inversodicraea bosii (C.Cusset) Rutish. & Thiv. ...
Continuing a survey of the chemistry of species of the largely continental African genus Vepris , we investigate a species previously referred to as Vepris sp. 1 of Congo. From the leaves of Vepris sp. 1 we report six compounds. The compounds were three furoquinoline alkaloids, kokusaginine (1), maculine (2), and flindersiamine (3), two acridone alkaloids, arborinine (4) and 1-hydroxy-3-methoxy-10-methylacridone (5), and the triterpenoid, ß-amyrin (6). Compounds 1–4 are commonly isolated from other Vepris species, compound 5 has been reported before once, from Malagasy Vepris pilosa , while this is the first report of ß-amyrin from Vepris . This combination of compounds has never before been reported from any species of Vepris . We test the hypothesis that Vepris sp. 1 is new to science and formally describe it as Vepris teva , unique in the genus in that the trifoliolate leaves are subsessile, with the median petiolule far exceeding the petiole in length. Similar fleshy-leathery four-locular syncarpous fruits are otherwise only known in the genus in Vepris glaberrima (formerly the monotypic genus Oriciopsis Engl.), a potential sister species, but requiring further investigation to confirm this phylogenetic position. We briefly characterise the unusual and poorly documented Atlantic coast equatorial ecosystem, where Vepris teva is restricted to evergreen thicket on white sand, unusual in a genus usually confined to evergreen forest. This endemic-rich ecosystem with a unique amphibian as well as plants, extends along the coastline from the mouth of the Congo River to southern Rio Muni, a distance of about 1,000 km, traversing five countries. We map and illustrate Vepris teva and assess its extinction risk as Endangered (EN B1ab(iii)+B2ab(iii)) using the IUCN, 2012 standard. Only three locations are known, and threats include port and oil refinery construction and associated activities, with only one protected location, the Jane Goodall Institute’s Tchimpounga Reserve. Initial evidence indicates that the seeds of Vepris teva are dispersed by chimpanzees, previously unreported in the genus.
... Global extinctions in tropical Africa are increasing. Apart from those recorded in Humphreys et al. (2019), additional global plant species extinctions have been recently recorded in the areas where the taxa treated in this paper are concentrated: the Cross-Sanaga Interval (Cheek & Williams 1999;Cheek et al. 2018b;2018c;2019c), in the EACF of Tanzania (Cheek & Luke 2022) and in Gabon (Moxon-Holt & Cheek 2021;Cheek et al. 2021a). This makes it imperative to seek measures to protect these highly (which was not certified by peer review) is the author/funder. ...
... Cola metallica was one of three new species to science of Cola that came to light (Cheek, 2002) as a result of botanical surveys on and around Mt. Cameroon (Cheek 1992, Thomas & Cheek 1992, Cheek et al. 1996 which culminated in The Plants of Cameroon, a conservation checklist (Cable & Cheek 1998). Additional rare and threatened species discovered to be new to science in these surveys include Octoknema mokoko Gosline & Malécot (Gosline & Malécot 2012), Oxygyne duncanii Cheek (Cheek et al. 2018c), Impatiens etindensis Cheek & Eb. Fischer (Cheek & Fischer 1999), Impatiens frithii Cheek (Cheek & Csiba 2002), Ancistrocladus grandiflorus Cheek (Cheek 2000) and most recently Drypetes burnleyae Cheek (Cheek et al. 2021b). ...
A new subgenus, Subg. Disticha is erected for 14 species of simple-leaved Cola sharing unique characters within the genus which are presumed synapomorphies: distichous phyllotaxy; petioles lacking pulvini; petioles of uniformly short length, <10 mm long; male flowers with short androphores <1(- 2) mm long; stamens 4 - 5; stem indumentum where present, dominated by short simple translucent hairs (except in C. philipi-jonesii where stellate), and in many species dark purple to black stems with contrasting bright white lenticels. All species have fruit with small globose, unsculptured orange mericarps c. 1 cm diam. (where fruits are known). The species of this subgenus range from SE Nigeria in the west to coastal Kenya and Tanzania in the east and Malawi in the south, but are absent from the Congo basin. Species diversity is highest in the Cross-Sanaga and Eastern Arc-Coastal Forest biogeographic areas, consistent with these taxa being Pleistocene refuge species. The species are mainly monoecious, but dioecy cannot yet be ruled out in some species. In two species where sufficient material was available for investigation (Cola chlorantha, C. roy), the simple cymes were found to be bisexual, the terminal flower being female, the two lateral flowers often being male, a pattern previously unreported in the genus. All species are understorey shrubs or small trees of evergreen lowland or submontane forest, except C. uloloma of coastal semi-deciduous forest in E Africa and which is unique in showing xerophilic characteristics. The species can be divided into group A: five species mainly in E Africa with rapidly glabrescent or glabrous stems, conspicuously asymmetric leaves, few-flowered, pedunculate cymes (C. uloloma, C. chlorantha, C. roy sp.nov., C.udzungwa, C. asymmetrica sp. nov.); group B: in Lower Guinea (Atlantic coast of Africa) with hairy stems, symmetric or inconspicuously asymmetric leaves, sessile, fasciculate inflorescences: (Cola mayimbensis, C. philipi-jonesii, C. metallica, C.moussavoui, C. stigmatosa, C. takamanda sp.nov. C. toyota sp. nov, C. campo-maan, C. zanaga sp. nov.). Of the seven new species to science, two are named informally since the material is so incomplete (sterile), and five are formally named. Species diversity is highest in Cameroon and Tanzania, each with four species, followed by Gabon with three species. It is expected that additional new species will be found in poorly-surveyed surviving evergreen forest habitat in each of these three countries. Conservation assessments are given for each species using the IUCN 2012 standard. All species are considered threatened, with ten species being Critically Endangered (the highest category of threat), each known from a single location, with their forest habitat threatened mainly by clearance for agriculture.
