Kupeantha yabassi (Coffeeae- Rubiaceae), a new Critically Endangered shrub species of the Ebo Forest area, Littoral Region, Cameroon

A new species to science of evergreen forest shrub, Kupeantha yabassi (Coffeeae - Rubiaceae), is described, illustrated, mapped, and compared morphologically with the closely similar species K. pentamera. Restricted so far to a single site in evergreen lowland forest near the Ebo Forest, Yabassi, Littoral Region, Cameroon, this species is Critically Endangered using the IUCN 2012 standard due to habitat clearance driven mainly by agriculture, adding to the growing list of threatened species resulting from anthropogenic pressure on Cameroon forests. A revised key to the six species of Kupeantha is presented. Two distinct geographical and ecological species groupings within the genus are identified and discussed. Notes are given on other narrowly endemic and threatened species in the Ebo forest area, a threatened centre of diversity important for conservation in Littoral Region.


Introduction
The new species reported in this paper was discovered as a result of a long-running survey of plants in Cameroon to support improved conservation management. The survey is led by botanists from the Royal Botanic Gardens, Kew and IRAD (Institute for Research in Agronomic Development)-National Herbarium of Cameroon, Yaoundé. This study has focussed on the Cross-Sanaga interval (Cheek et al. 2001(Cheek et al. , 2006 which contains the area with the highest plant species diversity per degree square in tropical Africa (Barthlott et al. 1996). The herbarium specimens collected in these surveys formed the foundations for a series of Conservation Checklists (see below). So far, over 100 new species and several new genera have been discovered and published as a result of these surveys, new protected areas have been recognised and the results of analysis are feeding into the Cameroon Important Plant Area programme (https://www.kew.org/science/our-science/projects/tropical-important-plantareas-cameroon), based on the categories and criteria of Darbyshire et al. (2017).
During completion of a paper erecting the genus Kupeantha Cheek (Cheek et al. 2018a), it was noted that a specimen, Leeuwenberg 6400 (K), included in the protologue of K. pentamera (Robbr. & Sonké) Cheek (originally described as Calycosiphonia pentamera Robbr. & Sonké (Sonké et al. 2007), was geographically disjunct from all the other 38 specimens known of that species. Further investigation of this specimen, in connection with preparation of a Conservation Checklist of the Plants of the Ebo Forest, Littoral Region, has

Taxonomic treatment
Kupeantha yabassi can be distinguished from K. pentamera which it is most closely similar to, and most easily confused with, using the diagnostic characters presented in Table 1, below. It can be distinguished from all other species of the genus using the key below.
DISTRIBUTION. Endemic to Cameroon (Map 1). Only known from a single collection made in forest near the Ebo Forest in the Littoral Region.
-100 km from the coast in Cameroon, indicates that the forest has been cultivated in the past (Letouzey 1957(Letouzey , 1960(Letouzey , 1968(Letouzey , 1985. At Ebo the geology is ancient, highly weathered basement complex, with some ferralitic areas in foothill areas which are inland, c. 100 km from the coast. The wet season (successive months with cumulative rainfall >100 mm) falls between March and November and is colder than the dry season (Abwe & Morgan 2008). CONSERVATION STATUS. Kupeantha yabassi is known from only a single site along the road parallel to the western boundary of the Ebo forest. Since 2006, botanical surveys have been mounted almost annually, at different seasons, over many parts of the formerly proposed National Park of Ebo. About 3000 botanical herbarium specimens have been collected, but this species has been seen not yet been seen in the c. 2000 km² of the Ebo Forest. However, much of this area, especially the western edge, has not yet been surveyed for plants. While it is likely that the species will be found at additional site likely including the Ebo Forest, there is no doubt that it is genuinely range-restricted. Botanical surveys and other plant studies for conservation management in forest areas north, west and east of Ebo resulting in thousands of specimens being collected and identified have failed to find any additional specimens of this species (Cheek et al. 1996;Cable & Cheek 1998;Cheek et al. 2000;Maisels et al. 2000, Harvey et al. 2004Cheek et al. 2004;Cheek et al. 2010;Harvey et al. 2010;Cheek et al. 2011). It is possible that the species is truly localised as are all other species of the genus west of the Sanaga (see discussion below). Kupeantha yabassi may well be unique to the Ebo Forest area, as are also, on current evidence, at least five other species (see discussion, below). The area of occupation of Kupeantha yabassi is estimated as 4 km² using the IUCN preferred cell-size. The extent of occurrence is the same. In February 2020 it was discovered that moves were in place to convert the forest into two logging concessions (e.g. https://www.globalwildlife.org/blog/ebo-forest-a-stronghold-for-cameroons-wildlife/ and https://blog.resourceshark.com/cameroon-approves-logging-concession-that-willdestroy-ebo-forest-gorilla-habitat/ both accessed 19 Sept. 2020). Such logging would result in timber extraction that would open up the canopy and remove the intact habitat in which Kupeantha yabassi is thought to grow. Additionally, slash and burn agriculture often follows logging trails and would negatively impact the population of this species. Fortunately the logging concession was suspended in August 2020 due to representations to the President of Cameroon on the global importance of the biodiversity of Ebo (https://www.businesswire.com/news/home/20200817005135/en/Relief-in-the-Forest-Cameroonian-Government-Backtracks-on-the-Ebo-Forest accessed 19 Sept. 2020). However, the forest habitat of this species remains unprotected and threats of logging and conversion of the habitat to plantations remain. Kupeantha yabassi is therefore here assessed, on the basis of the range size given and threats stated as CR B1+2ab(iii), that is Critically Endangered.

ETYMOLOGY.
Kupeantha yabassi named for the administrative centre nearest to the point where the specimen was collected.

VERNACULAR NAMES.
No vernacular names or uses are recorded.

NOTES.
Only known from the single collection cited. At Kew the specimen was annotated "indet. not matched in Tricalysia etc.", subsequently, loaned to BR in 1983 it was annotated by Robbrecht in 1986 as "unknown to me, I don't believe it belongs to Tricalysia"

Groupings within Kupeantha
The former placement of the only known specimen of Kupeantha yabassi in K. pentamera was understandable due to their morphological similarity. Both species have leaves of similar shape and size, and uniquely in the genus have tertiary nerves which are visible (they are inconspicuous in other species of the genus). They also share fruits of similar shape.
The six species of Kupeantha can be divided into two groups based on ecology and geography. The groups differ from each other also in sympatry and extent of occurrence.
1)East of the Sanaga river, the only two species documented are Kupeantha spathulata and K. pentamera. Both species are low altitude, predominantly occurring below 800 m (although the last has been recorded as high as 900 m). Both are known from numerous specimens 21 and 37 respectively, with numerous locations and large extents of occurrence (8105 km 2 , and 52 km 2 respectively). The two species are often sympatric, indeed have been collected in sequential number series at several of their common locations, in South Region,  ). These specimens are cited in the protologues of the two species Sonké 2010), they derive from a series of Rubiaceae-focussed surveys that resulted in numerous other discoveries of new Rubiaceae species to science, e.g., Sonké (2005Sonké ( , 2006. 2)West of the Sanaga River, the four species known, Kupeantha kupensis, K. fosimondi, K.ebo and K. yabassii are all upland, cloud forest species, occurring in the 800 -2000 m altitudinal range (However, Kupeantha ebo occurs in the range 770 -832 m). None are sympatric but allopatric, all are separated from each other by tens of kilometres. Even in the Ebo forest area, Kupeantha ebo and K. yabassi are physically separated by 20 km. These four species all have much smaller extents of occurrence (c. 8 km 2 in K. kupensis) and are much rarer and more localised (and so more threatened) than those species east of the Sanaga.
Despite the separation of these two groups, there is no evidence that they are separated phylogenetically. The two species East of the Sanaga are in fact so dissimilar that they were formerly placed apart from each other in separate genera (Calycosiphonia and Argocoffeopsis, Sonké 2010 respectively).

Kupeantha yabassi: its range and other endemic species in the Ebo Forest area.
Abwe & Morgan, (2008) and Cheek et al. (2018b) characterise the Ebo forest which is adjacent to the location of Kupeantha yabassi, and give overviews of habitats, species and importance for conservation. Fifty-two globally threatened plant species are currently listed from Ebo on the IUCN Red List website and the number is set to rise rapidly as more of Cameroon's rare species are assessed for their conservation status as part of the Cameroon TIPAs programme.  (Cheek et al. 2018a), Palisota ebo Cheek (Cheek et al. 2018b) and Pseudohydrosme ebo Cheek (Cheek et al. 2021).

Costus kupensis Maas & H. Maas (Maas-van der Kamer et al. 2016), Microcos magnifica
Cheek (Cheek, 2017), and Uvariopsis submontana Kenfack, Gosline & Gereau (Kenfack et al. 2003). It is considered likely that additional Kupe species may yet be found at Ebo such as Brachystephanus kupeensis I.Darbysh. (Champluvier & Darbyshire, 2009), Impatiens frithii Cheek (Cheek & Csiba 2002) since new discoveries are still frequently being made in the Ebo Forest area. Therefore, it is possible that Kupeantha yabassi might yet also be found in the Cameroon highlands, e.g. at Mt Kupe. However, this is thought to be only a relatively small possibility given the high level of survey effort at Mt Kupe: if it occurred there it is highly likely that it would have been recorded already.
Cameroon has been highlighted as the top country in tropical Africa for plant species diversity per degree square, and has high levels of endemism (Lachenaud et al. 2013;Onana 2011. The inventory of its Flora is far from completed, and the few remaining sizable areas of intact forest such as Ebo Forest, in the Littoral Region, are seriously threatened by clearance. Unfortunately, there is an increasing pressure to convert critical areas for biodiversity into oil palm plantations, and logging concessions (Mahmoud et al. 2019). As stated in the introduction, efforts are being made to delimit the highest priority areas in Cameroon for plant conservation as Tropical Important Plant Areas (TIPAs) (Darbyshire et al. 2017) to avoid the extinction of narrowly endemic species (Cheek et al 2018a;Mahmoud et al. 2019). However, the pressure for forest and wildlife resources is a stronger driver in the rapid decrease of primary forests and biodiversity. This paper contributes to documenting the rich flora of Cameroon and helps to highlight areas for conservation.
Such discoveries as this new species also underline the urgency for making such further discoveries while it is still possible since in all but one of the cases given, the range extension resulted from discovery of a new species for science with a narrow geographic range and/or very few individuals, and which face threats to their natural habitat, putting these species at high risk of extinction.
About 2000 new species of vascular plant have been discovered each year for the last decade or more. Until species are known to science, they cannot be assessed for their conservation status and the possibility of protecting them is reduced . Documented extinctions of plant species are increasing, e.g. Oxygyne triandra Schltr. and Afrothismia pachyantha Schltr. of South West Region, Cameroon are now known to be globally extinct (Cheek & Williams, 1999, Cheek et al. 2018c, Cheek et al. 2019). In some cases species appear to be extinct even before they are known to science, such as Vepris bali Cheek, also from the Cross-Sanaga interval in Cameroon (Cheek et al. 2018d) and elsewhere, Nepenthes maximoides Cheek (King & Cheek, 2020). Most of the >800 Cameroonian species in the Red Data Book for the plants of Cameroon are threatened with extinction due to habitat clearance or degradation, especially of forest for small-holder and plantation agriculture following logging . Efforts are now being made to delimit the highest priority areas in Cameroon for plant conservation as Tropical Important Plant Areas (TIPAs) using the revised IPA criteria set out in Darbyshire et al. (2017). This is intended to help avoid the global extinction of additional endemic species such as Kupeantha yabassi which we hope will be included in the proposed Ebo Forest IPA.
With only one locality known, Kupeantha yabassi represents another narrowly endemic Cameroonian species threatened with extinction due to deforestation for oil palm plantations, small-scale agriculture, mining and logging , Cheek et al. 2018a.