Bertiera sinoensis Jongkind ( Rubiaceae ) , a new forest liana from Liberia

Background: Fieldwork in Liberia in recent years has improved our knowledge of the local endemic species. Objectives: To describe a new species in  Bertiera to accommodate material from the south-east of Liberia that cannot be included in any known species. Methods: Existing herbarium collections were studied, the new species was studied in the field and the relevant published literature was consulted. Results: The new species  Bertiera sinoensis is described and illustrated here based on six specimens. Conclusions: The new species adds one more species to the botanical hotspot in south-east Liberia. It is assigned a preliminary conservation status of ‘Endangered’ (IUCN).


Introduction
Bertiera Aubl.(Rubiaceae) is a genus of ca.55 species from Africa, including Madagascar and the Mascarenes, and from America (World Checklist of Selected Plant Families [WCSP] 2016).Recently, several new African species have been published, as well as the taxonomic revisions for Cameroon and Madagascar (Nguembou et al. 2003(Nguembou et al. , 2006(Nguembou et al. , 2009;;Sonké et al. 2005;Wittle & Davis 2010).Recent phylogenetic research suggests that the genus is monophyletic, although less than 10% of its species have been sampled (Tosh et al. 2009).
Until now, there were only two climbing Bertiera species known, B. bracteolata Hiern and B. chevalieri Hutch.& Dalziel, and a third climbing species, B. sinoensis, is described here.The new species was first discovered in the herbarium by William Hawthorne when we were working on a guide to the forest trees, shrubs and lianes from Senegal to Ghana (Hawthorne & Jongkind 2006).Recently, several more specimens have been studied and collected in the field by the author and his team.

Research method and design
All relevant herbarium collections at the BR, K, P and WAG herbaria were examined.Bertiera sinoensis has recently been studied in the field on several occasions.Preliminary assessment of the International Union for the Conservation of Nature (IUCN) Red List categories was performed and species according to the criteria through the RBG Kew website (http://geocat.kew.org).

Taxonomic treatment
Bertiera sinoensis Jongkind, sp.nov.Bertiera 'nimbae', Hawthorne & Jongkind (2006:618, 619).Objectives: To describe a new species in Bertiera to accommodate material from the south-east of Liberia that cannot be included in any known species.
Methods: Existing herbarium collections were studied, the new species was studied in the field and the relevant published literature was consulted.

Results:
The new species Bertiera sinoensis is described and illustrated here based on six specimens.

Conclusions:
The new species adds one more species to the botanical hotspot in south-east Liberia.It is assigned a preliminary conservation status of 'Endangered' (IUCN).

Etymology
The species epithet refers to the Sinoe River that runs through the area where the new species is found.

Ecology and distribution
Bertiera sinoensis is only known from the evergreen forest in south-east Liberia (Figure 2).), but the new species is restricted to south-east Liberia.The important taxonomic differences between these three species are summarised in Table 1.

Diagnosis
Apart from the inflorescence branching pattern, there is very little difference between B. bracteolata and B. chevalieri, and the relationship between the two taxa in Cameroon requires investigation.Bertiera bracteolata and B. chevalieri in Lower Guinea share the faint, closed pattern of very fine parallel veinlets on the lower side of the dried leaves, a pattern not seen on the leaves of the two taxa from Upper Guinea.
The fruits of B. bracteolata are often described as strongly ribbed (Hepper 1963:158), but this is only the case when they are dry and not when they are fresh (Figure 1c-d).From Guinea to Cameroon but not in Ghana, Togo and Benin

Conservation notes
Bertiera sinoensis is known from six locations.It is not known from protected areas but it is found close to Sapo National Park.Forest near some localities where it was previously collected has been transformed into oil palm plantations.With an extent of occurrence (EOO) of 1582 km2 and an area of occupancy (AOO) of 24 km2 (based on a cell width of 2 km), B. sinoensis is assigned a preliminary conservation status of 'Endangered' [EN B1b(i,ii,iii)+2b(i,ii,iii)] following IUCN Red List Categories and Criteria (IUCN 2015).
Photos by Jongkind
Bertiera sinoensis resembles B. bracteolata and B. chevalieri.All three are slender woody climbers with elongated inflorescences and are the only climbing species in the genus.The leaves of B. sinoensis are much more hairy and more slender than those of the other two species, the stipules and bracteoles are longer and more hairy, and the corolla is more conspicuously hairy.Both B. bracteolata and B. chevalieri are known from both Upper and Lower Guinea (sensu White 1979

FIGURE 2 :
FIGURE 2: Map showing the geographic distribution of B. sinoensis.