Notes on the endemic plant species of the Ebo Forest , Cameroon , and the new , Critically Endangered , Palisota ebo ( Commelinaceae )

During a visit to the Ebo forest of Littoral Region, Cameroon in April 2005, an unusually small, variegated species of Palisota was seen dominating the forest understorey over a 2 km section of footpath. Although many hundreds of plants were seen, all appeared sterile, lacking the conspicuous erect central flowering axis usual in the genus. Passing along this path the following year, a determined effort was made to investigate this species further. Uprooted plants revealed dull, yellow–brown berries that had been concealed in the soil under the leaves. Other plants yielded axillary flowering shoots/ inflorescences, with flowers in bud, unopened, at 7–8 a.m. About 10 fertile live plants were taken and placed in plastic bags for later investigation where, after several days, some produced open flowers, which, with the fruits were preserved in alcohol. This material provides the basis for the description of Palisota ebo Cheek below. Dimensions of floral, fruit and seed features are taken from the fluid preserved specimens, while other elements are described from the herbarium material and photographs taken in the field. The genus Palisota P.Beauv.


INTRODUCTION
During a visit to the Ebo forest of Littoral Region, Cameroon in April 2005, an unusually small, variegated species of Palisota was seen dominating the forest understorey over a 2 km section of footpath.Although many hundreds of plants were seen, all appeared sterile, lacking the conspicuous erect central flowering axis usual in the genus.Passing along this path the following year, a determined effort was made to investigate this species further.Uprooted plants revealed dull, yellow-brown berries that had been concealed in the soil under the leaves.Other plants yielded axillary flowering shoots/ inflorescences, with flowers in bud, unopened, at 7-8 a.m.About 10 fertile live plants were taken and placed in plastic bags for later investigation where, after several days, some produced open flowers, which, with the fruits were preserved in alcohol.This material provides the basis for the description of Palisota ebo Cheek below.Dimensions of floral, fruit and seed features are taken from the fluid preserved specimens, while other elements are described from the herbarium material and photographs taken in the field.
Placement of this species in Palisota in a West African context is confirmed by the fleshy, berried fruit, the absence of a 'spathaceous bract', the lack of perforated leaf sheaths and the presence of silky-hairy leaf margins (Brenan 1963).On a global basis, the floral morphology of petaloid sepals, 3 stamens attached in front of the petals and (2-)3 staminodes lacking anthers, attached in front of the sepals, place this species in Palisota (Faden 1998).Palisota is a genus of about 20 species restricted to the evergreen forests of subsaharan tropical Africa from Senegal in the west to Tanzania in the east (Faden 2007).The genus is most species-diverse in the forests of Cameroon and Gabon.Palisota includes the most massive species of Commelinaceae in Africa, including those with rosettes of leaves exceeding 110 cm long and 20 cm broad, shrub-like herbs 6 m tall, and fleshy lianas reaching 15 m high, mainly with large terminal inflorescences.Only three other species of the genus have axillary infloresences, these being P. bogneri Brenan, P. satabiei Brenan, and P. flagelliflora Faden (Brenan 1984, Faden 1995).All three also occur in the species-rich coastal forests of Cameroon and Gabon (Faden 1995).

The botanical importance of the Ebo forest
Ebo is a proposed National Park that is co-managed by the Ebo Forest Research Project (EFRP) and the Ministry of Environment and Forest (MINEF).It covers about 2000 km² of evergreen lowland and submontane forest with Podocarpus latifolius (Thunb.)RBr.ex Mirb.(B.Tchiengué pers.obs.) along numerous low, parallel ridges that run SSW-NNE, parallel to the line of the Cameroon Highlands which lie c. 100 km to the northwest.Ebo extends c. 50 km both north to south, and west to east, around the point of c. 4°22′N, 10°25′E (see map in Abwe & Morgan 2008).The geology is ancient, highly weathered basement complex, with some ferralitic areas in the south.Altitude ranges from c. 130 to 1115 m.In the region, rainfall is comprised between 2 and 3 m p.a. Annual mean rainfall was measured in 2010-2016 at two points within Ebo Forest: Bekob (2336 mm p.a.), and Njuma (3135 mm p.a.).The wet season (successive months with cumulative rainfall > 100 mm) was between March and November at both sites (Abwe & Morgan 2008, Abwe, Ebo Forest Research Program, Yaoundé, Cameroon, pers. comm. 2018).
Many small villages surround the Ebo forest, which until the late 1950s and early 1960s was inhabited mostly by the people of the Banen and Bassa tribes.The forest harbours eleven diurnal primate species including the Nigeria-Cameroon chimpanzee and a small population of gorillas of uncertain taxonomic affinity (Abwe & Morgan 2008).The high diversity and global conservation importance of the primates has driven the push to conserve Ebo against competing pressures of logging, oil palm plantations and mining.To date, the population of gorillas has attracted most attention, especially given the threats which they face (Gawaorecki 2016, Mowbray 2017).However, sampling of the plant life, while far from complete, indicates that the diversity and endemism levels of plant species is likely to be of similar or even greater global importance for conservation than that of the primates, perhaps exceeding that even of the Kupe-Bakossi area 100 km to the northwest.Surveys conducted in Kupe-Bakossi mainly in 1993-2002 resulted in 14 000 specimens, from which over 2412 plant species have been documented, of which 82 are endemic and 212 threatened with extinction using the IUCN standard (Cheek et al. 2004).
The Ebo forest was unsurveyed for plants until the dawn of the 21 st century, although several collections were made in the general Yabassi-Yingui area by the botanists Letouzey and, Leeuwenberg in the late 20 th century.This may be due to the comparative inaccessibility of Ebo by road, the lack of dramatic relief, and the greater attraction of the high peaks of the nearby mountains of the Cameroon line.
Our survey was conducted as part of the long-term survey of plants in Cameroon led by botanists from RBG, Kew and the National Herbarium of Cameroon (Cheek et al. 2006).This survey has focussed on the Cross River-Sanaga interval (Cheek et al. 2001) which contains the area with the highest species diversity per degree square in tropical Africa (Barthlott et al. 1996).The methodology for the surveys is detailed in Cheek & Cable (1997).To date 2875 herbarium specimens have been collected from Ebo with the intention that they will form the nucleus of data for a 'Conservation Checklist of the Plants of Ebo Forest', in the series that began with Mt Cameroon (Cable & Cheek 1998) and continued with Mt Oku and the Ijim Ridge (Cheek et al. 2000), Bali-Ngemba (Harvey et al. 2004), and Lebialem (Harvey et al. 2010).
New species to science discovered at Ebo as a result of the recent surveys to date are: Ardisia ebo Cheek (Cheek & Xanthos 2012) (Kenfack et al. 2003).
Most of these species are so far endemic to Ebo or its immediate neighbourhood, but a number of the submontane species are found to the West at Mt Kupe and the Bakossi Mts which are much more intensively surveyed (Cheek et al. 2004).These species are Costus kupensis, Microcos magnifica, Salacia nigra, Uvariopsis submontana, and extending to the Lebialem Highlands (Harvey et al. 2010), Myrianthus fosi.Additional species first thought to be endemic to Kupe-Bakossi (Cheek et al. 2004) that have subsequently been found at Ebo include Coffea montekupensis Stoff.(Stoffelen et al. 1997).
It is possible that with further surveys at Ebo, more of the numerous apparently endemic and threatened species of Kupe-Bakossi will be found at Ebo, such as Kupea martinetugei Cheek & S.A.Williams (Cheek et al. 2003), Ledermanniella onanae Cheek (2003), and Impatiens frithii Cheek (Cheek & Csiba 2002).
The number of flowering plant species known to science is disputed, with published figures varying widely depending on the method of estimation (Nic Lughadha et al. 2017), but a reasonable estimate is 369 000 (Nic Lughadha et al. 2016), while the number of species described as new to science each year has been fairly constant in the 21 st century, regularly exceeding 2000 (Kew R.B.G. 2016).
Approximately 5% of known plant species have been assessed for their global extinction risk following the IUCN (2012) 'gold standard' categories and criteria, with the results being published on the IUCN Red List.This number rises to 21-26% when evidence-based assessments beyond those on IUCN's global list are taken into account, and 30-44% of these assessments consider the species assessed to be threatened (Bachman et al. 2018).Newly discovered species such as that reported in this paper, are increasingly likely to be threatened, since widespread species tend to be discovered sooner.Although there are notable exceptions to this rule (e.g.Cheek & Etuge 2009), generally speaking, it is the more localised, rarer species that remain undiscovered.This makes it all the more urgent to discover, document and protect such species before they become extinct as is Oxygyne triandra Schltr.(Cheek & Onana 2011).Most of the Cameroonian species are threatened with extinction due to habitat clearance, mainly for small holder and plantation agriculture following logging (Onana & Cheek 2011, Cheek et al. 2018).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 more narrowly endemic species such as Palisota ebo.

MATERIAL AND METHODS
This study is based mainly on herbarium specimens and field observations made in Cameroon during a series of botanical surveys beginning in 1991 mainly led by the first author, which so far have resulted in 52 450 specimens being studied at K and YA, of which 37 850 were newly collected, the data stored on the Kew Cameroon specimen Access database (Cheek et al. 2004: 11).The top set of specimens was ini-tially deposited at SCA, and later YA, duplicates being sent to K. All specimens cited have been seen by the authors.Herbarium citations follow Index Herbariorum (Thiers continuously updated), nomenclature McNeill et al. (2012) and binomial authorities IPNI (continuously updated).Material of the suspected new species was compared morphologically with material of all other African Palisota, principally at K, but also using material from BM, P and US.The online search address used for retrieving specimen data from labels at P was https://science.mnhn.fr/institution/mnhn/collection/p/item/list?full_text=Palisota&higherTaxonomy_dynamic=genus&administrativeRegion_dynamic=stateProvince.The conservation assessment was made using the categories and criteria of IUCN (2012).Herbarium material was examined with a Leica Wild M8 dissecting binocular microscope fitted with an eyepiece graticule measuring in units of 0.025 mm at maximum magnification.The drawing was made with the same equipment using Leica 308700 camera lucida attachment.

RESULTS
The new species, Palisota ebo, appears to be most closely related to P. flagelliflora, sharing several features rare within the genus or unique to that species (Faden 1995): 1) inflorescence-bearing axillary shoots that lie on the forest floor and continue to produce additional inflorescences; 2) inflorescences composed of a single cincinnus; 3) long pedicels; 4) vertical flowers; 5) bearded filament in the unpaired stamen.
It is likely that the two taxa share a recent common ancestor.The two taxa can be separated using the characters shown in table 1.
Notes -Although common at the type locality within Ebo, Palisota ebo is absent from the rest of the forest.
We did not observe visitors to the flowers, nor did we see dispersal of the seeds.We can only speculate that day-flying insects are likely to effect pollination of the flowers, and that rodents consume the fruits (hidden as they are in the leaflitter) and might sometimes distribute the seeds.
Palisota ebo has potential as an ornamental indoor plant for conservatories in temperate climes, and as a shade-plant in the tropics.Its colourful variegated leaves make it eyecatching and attractive all year round.