An annotated checklist of vascular plants of Cherangani hills, Western Kenya

Abstract Cherangani hills, located in Western Kenya, comprises of 12 forest blocks, maintaining great plant diversity. However, little attention to plant diversity studies has been paid to it in the past years. Here, we present a checklist of the vascular plants of this region obtained through intensive field investigations and matching of herbarium specimens. In total, 1296 species, including 17 endemic species are documented, belonging to 130 families and 608 genera. This flora represents 18.50%, 43.83% and 54.17% of the Kenyan species, genera and families, respectively. The habit, habitat and voucher specimens, as well as brief notes on the distribution of each taxon recorded are presented in this checklist. It is the first exhaustive inventory of the terrestrial vascular plants in Cherangani hills which is a significant regional centre for plant diversity.


Introduction
One of the most critical issues on the global, regional and national agenda is the need to preserve biodiversity for future generations and concurrently strive to understand the indigenous knowledge of resource management practices (Nehal et. al. 2004). The concern for biodiversity preservation by government has highlighted the importance derived from broad and small scale vegetation (Whittaker et al. 1979;Frood and Calder 1987;Lunt 1990). Well managed forests are very useful in biodiversity conservation (Sayer et al. 1995). Conserving plant species of special interest in the tropical forest ecosystems ensures that the vital socio-economic and environmental services (e.g. soil and water conservation and wood and non-wood products) are in constant supply to the local communities living near these forests.
Much of the world's terrestrial plant diversity occurs in the tropical forests, where they are facing rapid deforestation (FAO 1997). Agricultural farming increased by 200% at the expense of the tropical forests between 1900and 1990(UNEP 2009a. Currently, many forests in the tropics are facing a myriad of threats including: unsustainable harvesting practices, illegal encroachment and degradation by the dependent communities (UNDP 2006). Over the last 20 years, the local inhabitants have encroached upon the forest land, converting it into settlement and farmlands (UNEP 2009a). Other factors contributing to the forest loss include change of ecological processes due to climate change, resulting in alteration of biogeochemical cycles and potential species loss (Wang et al. 2001). Moreover, the rapidly increasing human population is the main reason for the large forest loss in East Africa (Lung and Schaab 2009). In addition, ineffective forest policy implementation has also led to the biodiversity loss in Kenya.
The main goal of a checklist is the provision of high-quality baseline data of a given area or forest on all the accepted taxa. The collection of species resource information, namely species inventory, is the primary component of the biodiversity catalogue and the easiest to understand and operate (Heywood et al. 1997), with the nomenclature being the chief focus, as it is fundamental in the communication about plants and the key to biodiversity status. The process involves investigation, classification, ordering, quantification, mapping, analysis and synthesis of species information. Around the world, research on check listing of plants has been done or is on-going in various places (Chong et al. 2009). Although numerous botanists have collected plant specimens from Cherangani hills forest, no comprehensive species studies have been undertaken in all forest blocks (Synott 1979). In Kenya, numerous studies on plant checklists covering different regions have been undertaken on various ecological regions. Some of the major plant checklists include, Bura Tana River (Gachathi et al. 1994), Ol Ari Nyiro Range (Muasya et al. 1994), Mount Elgon (Tweedie 1976), Taita hills (Beentje 1988); (Thijs et al. 2013), Mount Nyiru (Bytebier andBussmann 2000), Shimba hills (Luke 2005), Kakamega forest (Fischer et al. 2010), Nandi Forests (Girma et al. 2015) and Mount Kenya (Zhou 2017). For Cherangani hills forest, few ad hoc expeditions resulted in several herbarium collections but failed to give the actual floristic listing, composition and distribution of the species (Blackett 1994).
The aim of this paper is to provide the first comprehensive checklist of the vascular species of Cherangani hills. The checklist will provide the basis for further studies of the indigenous species. It will also assist in implementing policies and strategies for the ecological research and conservation of this unique Highland forest ecosystem in Western Kenya.

Study site and current vegetation status
Cherangani hills are located in the western side of Kenya within an area defined by 1°16'N, 35°26'E and comprises 12 forest blocks, including Kapolet, Cheboyit, Chemurkoi, Embobut, Kaisungor, Kererr, Kipkunurr, Kiptaberr, Sogotio, Toropket, Kapkanyar and Lelan (UNEP 2009a) (Fig. 1). Within Cherangani hills, relatively undisturbed (nearly primary) forest, as well as disturbed, secondary forest, swamps and riverine forest and natural glades are present. Kapkanyar, Kapolet and Kiptaberr blocks compose the western block Forest Reserves and are comprised of bushland (Pratt et al. 1966), which have undisturbed forest ecology and together total approximately 20,000 ha. They are closed forests as there are no indications of human activity, hence there is a higher plant diversity, which is dominated by Aningeria-Strombosia-Drypetes forest, with a large area of mixed Podocarpus latifolius forest on the higher slopes. According to FAO (2010), all terrestrial ecosystems classified as primary forests are characterised as the most species-rich and diverse. This area is therefore classified as closed forest since it has a tree cover of 40% or more (UNEP et al. 2009b). To the east, forest reserves' blocks of Lelan, Embobut, Kererr, Kaisungor, Toropket, Chemurkoi, Kipkunurr, Cheboyit, Sogotio and Kapchemutwa are also comprised of woodland and grassland which are separate and have been interfered with by humans and domestic animals. Areas with vegetation cover other than forests, but are not under intensive land use, are defined as woodlands and are mostly used for cattle grazing (Holmgren 2006).
The forests on the south-eastern block along the escarpment crest are fragmented and separated by extensive natural grasslands, scrub and farmland especially in the central part. This area holds Juniperus-Nuxia-Podocarpus forest, with heavily disturbed Podocarpus falcatus forest on the eastern slopes. Generally, most of this area consists of middle-aged secondary forest, but much of it is characterised by very young secondary forest. This area is generally highly degraded and fragmented and the composition of plant communities has been greatly influenced by past commercial logging activities and other anthropogenic disturbances (Mitchell and Schaab 2008). Within the valleys in the upper peak areas, remnants of Juniperus-Maytenus undata-Rapanea-Hagenia forest could be found. Cyathea manniana occurs in the stream valleys and there are patches of Bamboo (Arundinaria alpina), even though there is no bamboo zone along the Cherangani hills. At higher altitudes, the forest is interspersed with a mixture of heath vegetation and swamps and the latter with Lobelia aberdarica, Senecio johnstonii and Dendrosenecio cheranganiensis. There are different types of vegetation especially in the east, with little obvious altitudinal zonation and an establishment of plantations of Cupressus lusitanica, Pinus patula and a few Eucalyptus species.

Specimen collection and identification
Between July 2015 and May 2018, the botanical team consisting of botanists from the National Museums of Kenya and Sino-Africa Joint Research Center held several explorations in the Cherangani hills. A combination of general walk-over survey method (Filgueiras et al. 1994) and a plotless landscape defined sampling methods for plant specimen collection and sight observation was used to aid the characterisation of the vegetation (Hall and Swaine 1981). Plant specimens bearing flower or fruit were collected and identified. Details of identified specimens were recorded. Specimen details included habit, habitat, distribution and collector details. The specimens were then preserved by pressing.
Voucher specimens were deposited at the East African Herbarium, Nairobi, Kenya (EA) and Herbarium of Wuhan Botanical Gardens, Wuhan, China), labelled with the plant's scientific name and common names, collection date, GPS coordinates, habitat, collector, identifier and a herbarium specimen number. Standard references were used for plant identification (FTEA 1952(FTEA -2012Blundell 1987;Agnew and Agnew 1994;Beentje 1994;Stewart and Campbell 2006;Agnew 2013).

Checklist
A comprehensive checklist of the vascular plant taxa of the Cherangani hills is enumerated below. Within this checklist, species are organised alphabetically in each family. The families are divided into four groups, namely lycophytes, monilophytes, gymnosperms and angiosperms. Families of lycophytes and monilophytes are organised based on the PPG I system (PPG I 2016), while those of gymnosperms are organised based on Christenhusz et al. (2011) and families of angiosperms are organised based on the APG IV system (APG IV 2016).

Families, genera and species diversity
The current checklist contains a total of 1296 vascular species belonging to 130 families and 608 genera that are indigenous, naturalised or introduced to Cherangani hills. This represents 18.50% of the total number of 7004 Kenyan vascular species obtained, 43.83% of the total number of 1387 Kenyan genera and 54.17% of the total number of 240 Kenyan families (MEWNR and RDA 2015). However, the number of species is still increasing because of the discovery of new records, new naturalised species and the introduction of invasive species.

Growth habit
The growth habit of Cherangani hills signifies that herbaceous species have the highest percentage of 54.39%. Herbs are plants without persistent woody stems. Shrubs are represented with 23.76% and can be defined as self-supporting woody plants branching at or near the ground or with several stems from the base or a single stem less than 2 m. A climber is also defined as a plant that grows upwards by attaching itself to other structures which it uses as support. A tree is a perennial woody plant with a secondary thickening, with a clear main trunk, is dependent on the single trunk and has a height of more than 3 m (Beentje 2016). Trees are also represented with 11.57% of the total species (Table 2). Plant species richness is usually higher in the herbaceous layer than in any other forest stratum. It is often stated that most plant biodiversity in the forest ecosystems is found in the herbaceous layer (Roberts 2004;Whigham 2004), which concludes that herbaceous flora in Cherangani hills has invaded most of the areas and hence has the highest percentage contributing to the high plant diversity.

Endemic and threatened species
There are 17 endemic plant species in Cherangani hills (Source FTEA), belonging to 5 families and 13 genera and accounting for 1.23% of the total species of which most are from the herb layer (Table 3). The region is not well protected, hence poses great danger to these species, for example, Dendrosenecio cheranganiensis is classified as a vulnerable species by IUCN (2013). In total, there are 34 threatened plant species (Source FTEA), belonging to 17 families and 28 genera representing 2.62% of the total plants in Cherangani hills (Table 4). Over-exploitation and habitat loss have led to species becoming rare and threatened, for example, Polyscias kikuyuensis is highly valued for its excellent timber, hence highly extracted.

New records
In the recent years, investigation researchers from Kenya and China have found many new species and several new records in Kenya, including, Sedum keniense (Crassulaceae) (Zhou et al. 2016a), Zehneria subcoraicea (Cucurbitaceae) (Zhou et al. 2016b), Z. longiflora (Cucurbitaceae) , Cissampelos keniensis (Menispermaceae) (Zhou et al. 2017b) and Adenia angulosa . So far, no new species from this region has been found, although, Parastriga alectroides (Scrophulariaceae), is recorded for the first time in Kenya, particularly in Cherangani hills. An updated description, comparisons with closely related species and revised conservation status for this species has been described.

Conclusion
Efforts to ensure the conservation of Cherangani forest vegetation habitat should be prioritised with much emphasis on the endangered, rare or endemic species, according to the checklist result. The adopted approach in these studies may help to focus on certain species and the setting of research and conservation priorities. The high proportion of Cherangani endemic species and the geographic rarity component of the flora associated with that of Mount Kenya and Mount Elgon plants, are aspects that makes these habitats interesting. Cherangani hills have not been inventoried exhaustively, including all of its 12 forest blocks. Our study provides the baseline data for further studies on the invasion process and on the patterns of biodiversity. More study approaches may also contribute to the identification of species which are threatened by anthropogenic impacts and therefore require protection. Community-based forest conservation is also suggested to ensure sustainable utilisation of these forests.

Checklist
The following lists of species include references to the elevation, and where metres are stated, this means metres above sea level. EA means the East African Herbarium, Nairobi, Kenya; HIB means the Herbarium of Wuhan Botanical Garden, Wuhan, China.