Biology subjects

Onana, J. M.

Publications and source records attributed to Onana, J. M..

9 recordsLinked to original sources

bioRxiv2025

Sericanthe etugei and S. onanae (Coffeeae Rubiaceae) new cloud forest tree species Endangered in Southwest Cameroon & Bioko (Equatorial Guinea).

Two new species of cloudforest tree are described and illustrated from the Cross-Sanaga Interval within the Lower Guinea Domain. Sericanthe etugei Cheek from South West and Littoral Regions of Cameroon is species from the Cameroon Highlands, and Sericanthe onanae Cheek from South West Region, Cameroon, and Bioko (Equatorial Guinea). Sericanthe etugei is similar to Sericanthe leonardii (N. Halle) Robbr. of DRC (Kivu) and Rwanda, differing in the stipular awn 0.25 mm long (vs 1 - 4 mm), the adaxial leaf midrib and secondary nerves glabrous (vs hairy), the tertiary nerves conspicuously scalariform with the naked eye (vs not visible). The species is also similar to Sericanthe testui var. testui, differing in being a tree (vs liana), with stems not decorticating (vs decorticating), the calyx truncate in bud (vs closed) and in the pubescent ovary (vs glabrous). Sericanthe onanae is similar to S. mpassa Sonke & Robbr. of lowland forest in Gabon, differing from that species in that the leaves have an acumen (0.5 - )0.7 - 0.8(- 1.2) cm long vs 0.3 - 0.5 cm, secondary nerves are 7 - 10 (- 12) on each side of the midrib (vs 4 - 6 in S. mpassa), and that the stipules are 5 - 6.5( - 7) x 3 - 5(- 6) mm ( vs 2.5 mm long) and truncate (vs overtopped by an awn c. 1 mm long). It is also similar to S. jacfelicis (N. Halle) Robbr., differing in that the leaves are smaller (<15 cm long vs 16 - 20 cm long), the abaxial surface of the leaf blade has 7 - 10( -12) lateral nerves on each side of the midrib (vs 5 -7) and has a glossy surface and papery texture (vs matt, coriaceous), the petioles are hairy (vs glabrous), the stipules are 5 - 6.5( - 7) mm long, truncate, lacking an awn or arista, (vs 3 -4 mm long, with an arista 0.5 - 1 mm long). These two new species are both provisionally assessed as Endangered EN B2ab(iii) with the 2012 IUCN standard. The new species are briefly discussed in the context of other newly discovered submontane species from the Cross-Sanaga Interval. We speculate that the seeds of these species may be primate-dispersed.

plant biology↗

bioRxiv2024

Keetia nodulosa sp. nov. (Rubiaceae - Vanguerieae) of West - Central Africa: bacterial leaf nodulation discovered in a fourth genus and tribe of Rubiaceae.

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), Sericanthe (Coffeaeae) and Pavetta (Pavetteae). 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.

plant biology↗

bioRxiv2023

A new cloud forest tree Lychnodiscus bali (Sapindaceae), Critically Endangered from the Bali-Ngemba Forest reserve, N.W. Region, Cameroon.

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.

plant biology↗

bioRxiv2022

A new Critically Endangered cloud forest tree Microcos (Grewiaceae-Malvaceae) from the Rumpi Hills of S.W. Region Cameroon.

We describe Microcos rumpi (Grewiaceae-Malvaceae) as a new species to science from the Rumpi Hills of SW Region Cameroon, a proposed Tropical Important Plant Area. Confined on current evidence to submontane forest, the species is threatened by expanding habitat clearance for farms and is assessed as Critically Endangered. A massive tree, attaining 35 - 40 m height, and 80 cm trunk diameter at 1.3 m above ground, its biomass is calculated as in the range of 7 - 8 metric tonnes. It is the third tree species of the genus recorded from Cameroon and only the fourth recorded west of D.R. Congo. A key to these four species is presented. The concept of Microcos in Africa in relation to Grewia is discussed, and three new combinations are made, transferring three species names from Grewia to Microcos: Microcos louisii (Wilczek) Cheek, M. evrardii(Wilczek) Cheek and M.schmitzii (Wilczek) Cheek.

plant biology↗

bioRxiv2022

Monanthotaxis bali (Annonaceae) a new Critically Endangered (possibly extinct) montane forest treelet from Bali Ngemba, Cameroon

Monanthotaxis bali is the only known, solely montane (occurring solely above 2000 m alt.) species of the genus. It joins Monanthotaxis orophila (Rwanda) and M. discolor (Tanzania), two other species that can also occur above 2000 m alt. Monanthotaxis bali is an addition to the small number (28) of the tree species of the surviving montane forests of the Cameroon Highlands of which only eight other species are endemic. Due to its supra-axillary inflorescences, and petals arranged in one whorl but with the outer petals overlapping the inner petals distally, and rounded flower buds, the new species is placed in Hoekstras clade B of Monanthotaxis. The new species is unusual in being a treelet in a predominantly lianescent genus, and in lacking the glaucous underside of the leaf-blades that usually characterises the genus. Monanthotaxis bali takes the number of continental African species of the genus to 80, and makes Cameroon, with 30 species, the most species-diverse country for the genus. Monanthotaxis bali is known only from the Bali Ngemba Forest Reserve, a forest remnant under pressure of degradation and clearance in the Bamenda Highlands of Cameroon. It may already be extinct due to logging and agricultural activities. Here it is described, illustrated, mapped and assessed as Critically Endangered (Possibly Extinct) using the IUCN 2012 criteria.

plant biology↗

bioRxiv2022

Impatiens banen sp. nov. & I. etugei sp. nov. (Balsaminaceae), threatened lowland species of the Cross-Sanaga Interval, Cameroon

We describe two range-restricted new species to science from the genus Impatiens (Balsaminaceae), both threatened, from the Cross-Sanaga Interval of western Cameroon. The first, Impatiens banen, appears to be restricted to an open seepage microhabitat on granitic inselbergs in the lowland-submontane forest zone of the Ebo Forest in Littoral Region and is provisionally assessed using the 2012 IUCN standard as Vulnerable. Sharing characters with Impatiens burtonii and I. mannii, it differs from both, and appears to be unique in Cameroon inter alia 1) in the bicolored united lateral petals, the upper petals being white, while the lower petals are an intense pink-purple, 2) the hairy, filamentous spur, purple with a white apex, is curved along its length (through nearly 360{degrees}), almost describing a circle. Inselberg-specific species are unusual in Impatiens. The second species, Impatiens etugei, of the I. macroptera aggregate, is restricted to rocks in the Mutel River of the Kom Wum Forest Reserve of NorthWest Region and is assessed as Critically Endangered. Having similarities with I. mackeyana and I. letouzeyi, it differs from other species in the aggregate inter alia by having opposite leaves (vs always alternate), flower exterior white (vs pink or pink-purple), and in the dorsal petal having a pair of lateral projections (vs projections absent).

plant biology↗

bioRxiv2021

The endemic plant species of Bali Ngemba Forest Reserve, Bamenda Highlands Cameroon, with a new Endangered cloud-forest tree species Vepris onanae (Rutaceae).

We revise and update the records of strict and near-endemic species of the Bali Ngemba Forest Reserve, the largest known surviving patch (c. 8 km2 in area) of submontane or cloud forest in the Bamenda Highlands, Cameroon which have lost >96 % of their original forest due to human activities. Nine strict endemics, and 11 near endemics are now documented, a drop from the number recorded after the first survey in 2004, since when five of the provisionally named species have been formally published. We test the hypothesis that a further one of the provisionally named putative Bali Ngemba new species, Vepris sp. A, an 8 - 20 m tall tree from cloud forest in the 1310 - 1600 m altitudinal band, is indeed new to science. We compare it morphologically with other multicarpellate, apocarpous, trifoliolate Cameroon tree species formerly placed in the genus Oricia Pierre until they were subsumed into Vepris by Mziray (1992). These are Vepris trifoliolata (Engl.) Mziray and V. gabonensis (Pierre) Mziray. We conclude that Vepris sp. A is a new undescribed species here named as Vepris onanae. The new species is illustrated, mapped and its conservation status assessed as Endangered using the 2012 IUCN standard due to the threats of habitat clearance from agricultural pressures at its three locations all of which remain formally unprotected. Vepris onanae appears unique among the Guineo-Congolian African oricioid species of Vepris in occurring in cloud forest, the other species, apart from V. renierii of the Albertine Rift, occurring in lowland forest. It also differs in the very broad, (7.8 -) 11.3 - 18 cm wide leaflets of the flowering stems which have a 6-18(-30) mm long, narrowly triangular acumen (vs leaflets <12 cm wide, acumen absent or short) and in having both subsessile and pedicellate (pedicels 0.25 - 0.3 mm long and 1(- 2) mm long) male flowers (vs male flower pedicels all sessile, or all c. 3 mm long). We report for the first time on stage-dependent leaf heteromorphy in Vepris and characterise a level of sexual dimorphism more advanced than usual in the genus. We highlight the importance of protecting Bali Ngemba and other forest patches in the Bamenda Highlands if species such as Vepris onanae are not soon to become extinct.

plant biology↗

bioRxiv2021

Uvariopsis ebo (Annonaceae) a new, Critically Endangered tree species from the Ebo Forest, Cameroon and a key to the Cameroonian species of Uvariopsis

A new species to science of evergreen forest tree, Uvariopsis ebo (Annonaceae) is described, illustrated, mapped, and compared morphologically with the other cauliflorous species of the genus. Restricted so far to a single site in evergreen lowland forest in the Ebo Forest, Yabassi, Littoral Region, Cameroon, this species is Critically Endangered using the IUCN 2012 standard, because the forest habitat of this species remains unprotected, and there exists threats of logging and conversion to plantations. This species adds to the growing list of threatened species resulting from anthropogenic pressure on Cameroon forests. Observations on the unusual corolla structure of the new species are made. A revised key to the 14 Cameroonian species of Uvariopsis is presented. Notes are given on other narrowly endemic and threatened species in the Ebo forest area, a highly threatened centre of diversity in Littoral Region, globally important for conservation.

plant biology↗

bioRxiv2020

Deinbollia onanae (Sapindaceae), a new, Endangered, montane tree species from the Cameroon Highlands.

Deinbollia onanae (Sapindaceae-Litchi clade) is here formally named and characterised as a new species to science, previously known as Deinbollia sp. 2. Cameroon has the highest species-diversity and species endemism known in this African-Western Indian Ocean genus of 42 species. Deinbollia onanae is an infrequent tree species known from five locations in surviving islands of montane (or upper submontane) forest along the line of the Cameroon Highlands. It is here assessed as Endangered according to the IUCN 2012 standard, threatened mainly by clearance of forest for agriculture. The majority of tree species characteristic of montane forest (above 2000 m alt.) in the Cameroon Highlands are also widespread in East African mountains (i.e. are Afromontane). Deinbollia onanae is one of only a very small number of species that are endemic (globally restricted to) the mountain range. It is postulated that this new species is in a sister relationship with Deinbollia oreophila, which is a frequent species of a lower (submontane) altitudinal band of the same range. It is further postulated that seed dispersal is or was by frugivorous birds, potentially turacos, alternatively by primates such as Preuss s monkey.

plant biology↗