1. Introduction

Plant diversity is relatively high in Kenya with approximately 6881 plant species occurring in different ecosystems (Zhou et al., 2017). These plant population is constantly decreasing due to effects of climate change and as a result of anthropogenic activities (Millar et al., 2007). Therefore, the government is instituting conservation efforts through legislations and different government agencies that are mandated to manage the environment and biodiversity. The legislations include Kenya Wildlife Conservation Management (The Constitution of Kenya, 2010; Government of Kenya, 2012b, 2013), National Environment Management Authority (NEMA) (Government of Kenya, 2012a) and Kenya Forest Service (KFS) (Government of Kenya, 2017).

Botanic gardens provide for ex situ conservation and a means for achieving plant diversity and conservation (Thormann et al., 2006; World Health Organization, International Union for Conservation of Nature and Natural Resources & World Wide Fund for Nature, 1993; Wyse Jackson & Sutherland, 2000). The Botanic gardens constitute documented collections of living plants for purpose of scientific research, conservation, display and education (Hawkins, 2008; Oldfield, 2009). Globally, there are about 1846 botanical gardens and more than 30% of them are owned by Universities and other research institutions for higher education. Less than 40% of botanic gardens are found in tropical regions of the world. Despite the fact that the tropics are characterized by high biodiversity and endemism, the region has faced high rate of threats due to climate change and human activities in the recent past (Prance et al., 2000).

In Kenya, there are more than twelve botanic gardens which include the Kaya Cum Arboretum in Bamburi (Mombasa County), Moi University Botanic Garden in Eldoret, East African Agriculture and Forestry Research Institute (KARI) in Muguga. The Baobab Gardens in Kilifi, Mutomo Hill Plant Sanctuary in Kitui, Mazeras Botanical Gardens/Nursery in Mombasa County, Nairobi Arboretum and the Nairobi Botanic Garden of the National Museums of Kenya in Nairobi County, Pwani University botanical garden in Kilifi County, Egerton University in Nakuru County, Jomo Kenyatta University and Mount Kenya University, Kiambu County (Anonymous, 2018a, 2018b, 2018c; Omondi & Omondi, 2015; Misonge et al., 2016). Other Universities in Kenya such as Kenyatta University and University of Nairobi in Nairobi County and Kenya Methodist University in Meru County have botanic gardens whose flora largely remains undocumented.

Mount Kenya University Botanic Garden is a member of Botanical Gardens Conservation International (BGCI) which constitute a network of 500 gardens (Botanic Gardens Conservation International, 2018). The network spearheads inter-botanical gardens collaborations with the aim of documenting and mitigating the impacts of global climate change (Primack & Miller-Rushing, 2009). Such programs, among others, in turn, provide important models for establishing specific strategies to protect valuable plant species from extinction (Donaldson, 2009).The current study seeks to develop a check list of plants of Mount Kenya University Botanic Garden to serve as a guide for research and education. The list shall also be important in prioritizing conservation of rare, endemic and vulnerable indigenous plant species.

2. Material and Methods

Study area

The study was carried out at the Mount Kenya University botanic garden in Thika, Kiambu County (Figure 1). The garden covers an area of 78 000 m² (19.27 acres). The site is geo-referenced with the GPS coordinates: 1°3'2"S, 37°8'9" E, 1°3'4"S, 37°8'22"E, 1°3'8"S, 37°8'6"E and 1°3'9"S, 37°8'24"E. The Botanical Garden lies at elevations between 1432.56 meters to 1459.38 meters above the sea level and has a bimodal rainfall pattern. The average annual rainfall in Thika and its environs ranges between 900 mm and 1250 mm per annum. The climate is moderate tropical with sunshine most of the year round and typical average temperatures of 25°C during the day, with the hottest period in January - February leading to the long rains, March - May and a spell of cold weather in July. The land has a gradual slope from South to the North. Although the vegetation zoning of Kiambu County is largely characterized by highlands climate, the outskirts of Thika sub-county, where the Botanical garden is situated, is notably a gradual transition into the wooded bushed grasslands vegetation type towards the semi-arid South East of the country.

Figure 1. Map of Thika Constituency Showing the position of Mount Kenya University Botanic Garden at Happy Vally in the Left and map of Kenya showing the position of Kiambu County on the Right

Topography, geology and soils

Thika sub-county lies at the Athi-Kapiti plains (Masai plateau), close to the central highlands. The Mount Kenya University botanic garden is situated in the Eastern part of Thika Town. The topography of the town is characterized by relatively flat plains with a gentle slope of between 5°-10° from East to West at an altitude of 1200 - 1360 meters above sea level. There are small valleys on the western and northern edges following the Chania and Thika Rivers that have waterfalls and meet on the northwestern edge of Thika Town. The soils are dissected and easily eroded. Moreover, they are low fertility sandy and clay soils (County Government of Kiambu in Collaboration with Ministry of Land Housing and Urban Development, 2015).

Local population and vegetation

Thika town is an industrial and business town of Kenya. According to the census of 2019, Thika has a population about 200,000 people (“http://worldpopulationreview.com/countries/kenya-population,” 2019). The Mount Kenya University botanic garden is situated next to Happy valley and Landless estates in Thika. The estates are medium density residential area with about 32 dwellings per hectare. The site for the botanical garden was neglected quarry land after mining of building stones. The botanical garden therefore was a landscape restoration strategy that was meant to create long standing habitat protection and provision of human insecurity against landslides. The vegetation is found as patches of grassland, woodlands and riparian. Generally, the vegetation surrounding the area of study is persistently threatened by land subdivisions, quarrying, and clearance for settlements, agriculture and exploitation for medicinal plants (County Government of Kiambu in Collaboration with Ministry of Land Housing and Urban Development, 2015).

Study design

Observational design was used in this study. Regular field trips were conducted to the study site for a period of five years from January 2012 to December 2017. Two methods were used to develop the list of plants. First, physical identification and enumeration of the plants, which was done by walking around the botanic garden and secondly, line transect and point centered quadrant (Misonge et al., 2016).

Plant identification and documentation

Reconnaissance survey was done before actual study for this work. It was necessary for general familiarization and understanding of the vegetation of the study site. It also formed a basis for deciding the suitable methods of data collection. Regular field trips were conducted in the study area for a period of five years from January 2012 to December 2017. Two methods were used to develop a list of plants, physical identification a group and counting of the plants, which was done by walking in the botanical garden. The identity of the plant specimens was confirmed at the East African Herbarium, National Museums of Kenya.

3. Results and Discussion

Floristic analysis

A total of 223 plant species in 57 families of seed-bearing plants, comprising trees, shrubs and herbs were recorded (Table 1). Out of the total number of families recorded, only three had more than 10 species while 21 families had one species each. The class Gymnospermae (cone-bearing plants) was represented by a single, exotic species, Cupressus lusitanica. Angiospermae (flowering plants) had 57 families; 51 dicotyledons and 6 monocotyledons. Poaceae, the grass family, dominated the herb layer with 30 species followed by Asteraceae (sunflower family) with 18 species. Trees were dominated by the genus Acacia with 8 species followed by Ficus with 6 species. Three species namely Ficus scassellatii ssp. thikaensis voucher number KMB002/2019 is known to be ENDEMIC in Thika (Kenya) (van Noort & Rasplus 2019), Pavetta teitana voucher number KMBU003/2019 and Combretum tanaense with voucher number KMB01/2019 are reported as RARE and VULNERABLE (Walter & Gillett, 1998) respectively, and therefore require to be prioritized for conservation.

Table 1. Frequency of species per family

Plant checklist

A checklist of trees, shrubs and herbs of the proposed Mount Kenya University Botanic Garden was compiled as the major output of this study (appendix 1). The checklist is arranged alphabetically by family and then by genus and species under each family. Synonyms are in square brackets. The list was compiled using multiple taxonomic data available (Beentje, 1994; Dharani et al., 2010; Gachathi, 2007; Gibbs Russell et al., 1991; Graf, 1978; Ivens, 1967; Kokwaro, 2009, Turril, W.B. & Milne-Redh. & others (eds.) 1952-2015 and later confirmed at the East African Herbarium, National Museums of Kenya, Nairobi and the African Plants Database.

Identification of unique plants

Pavetta teitana, Ficus scassellatii ssp. thikaensis and Combretum tanaense, were recorded in this study as unique because they are rare, endemic or threatened. In a study done by Malombe & Mutangah (2005) at thirteen sites in Thika district, Pavetta teitana, Ficus scassellatii ssp. thikaensis) were identified in habitats that were away from Thika or Chania river. Pavetta teitana and Ficus scassellatii ssp thikaensis were recorded in three sites that were David Harries and Kuraiha forests. On the other hand, Combretum tanaense, a vulnerable plant species, which is endemic and indigenous in Kenya (Walter & Gillett, 1998) was recorded for the first time as a riparian vegetation along Chania River. The listing of C. tanaense among other plants at Mount Kenya University botanic garden flora provides an additional site where this unique species occurs in Thika.

4. Conclusions

It was concluded that the botanical garden Mount Kenya University botanic garden support the goal of the county in protecting, preserving and managing environmental and natural resources for socio-economic development. The list also provides a basis for research and conservation of indigenous plants.

ACKNOWLEDGEMENTS

The authors express their gratitude to Mount Kenya University for setting aside about 1% of its land for conservation purposes. Tribute also goes to Mungai Geofrey M. of National Museums of Kenya for plant authentication. Finally, the authors thank Gachathi M.N.F for carrying out a pre-review and editing the final manuscript fort this paper.

Appendix

Appendix 1. A Plant Checklist arranged alphabetically by families