Kenya, an African country with major higher plant diversity, has a corresponding diversity of plant associations, because of the wide geographic distribution, diverse climatic conditions and soil types. In this article, all vascular plants of Kenya were counted based on the completed "Flora of Tropical East Africa (FTEA)", and all families and genera were revised using recent molecular systematics research, forming a "Synoptic List of Families and Genera of Kenyan Vascular Plants (SLFGKVP)". In total, there are 225 families, 1538 genera and 6293 indigenous species and and 62 families, 302 genera and 588 exotic species in Kenya. The Fabaceae with 98 genera and 576 Species is the largest family. Two of the seven plant distribution regions of Kenya, K4 and K7 are the most species-richest areas with regard to both total and endemic species, with 3375 and 3191 total species and 174 and 185 endemic species in K4 and K7 respectively. While, K3 and K5 have the highest density of both total and endemic species. K1 has the lowest density of total species, and K2 has the lowest density of endemic species.

East Africa, Kenya, FTEA, vascular plants, molecular systematics, diversity

The Republic of Kenya (Fig. 1) lies in the equatorial zone of eastern part of Africa continent, between latitudes 4°N and 4°S and between longitudes 34°E and 42°E. It is bordered by Tanzania to the south, Uganda to the west, Ethiopia to the north, Sudan to the north-west, Somalia to the east, and the Indian Ocean to the south-east (Orodho 2006). Kenya covers a total area of 582,646 km², including 569,253 km² land area and 13,393 km² water area. The equator runs through the central part of Kenya, intersecting the Great Rift Valley, forming the famous "East Africa Cross". Mt. Kenya is the largest ancient extinct volcano in Great Rift Valley areas. It is the highest mountain of Kenya and the second highest in Africa with a height of 5,199 m a.s.l. (the first one being Mt. Kilimanjaro, 5,892 m a.s.l.) (Ojany and Ogendo 1973, Speck 1982, Sombroek et al. 1982, M,U 2009).

According to the early administrative division of Kenya, seven plant distribution regions (K1–K7) had been divided by "Flora of Tropical East Africa" (hereafter FTEA) (FTEA editors 1952–2012) (Fig. 1). K1 represents the "Northern Frontier Province" which is located in the northern part of Kenya. K2 represents the "Turkana Province" which is located in the northwest part of Kenya. K3 represents the "Rift Valley Province" which is located in western part of Kenya. K4 represents the "Central Province" which is located in central part of Kenya. K5 represents the "Nyanza Province" which is located in southwest part of Kenya. K6 represents the “Masai Province” which is located in southern part of Kenya. K7 represents the "Coast Province" which is located along the coastal area of Kenya (Polhill 1988).

Figure 1. 

Kenya and its location. K1–K7 indicates plant distribution regions in "Flora of Tropical East Africa" (FTEA editors 1952–2012).

The soils of Kenya are diverse ranging from the coral types on the coastal areas to the alluvial, swampy, and black cotton soils along river valleys and plains, to abundant volcanic soils on the high mountain regions (Orodho 2006). Climatically Kenya is considered part of the tropical monsoon area belonging to the tropical savanna climate region, and the annual maximum temperature is from 22 to 26 °C, and annual minimum is from 10 to 14 °C (Gao 2004). Rainfall patterns varies with different seasons around the year, that is, most parts experience high rainfall from March to June and October to December, and the rest are dry spells. Annual rainfall from the southwest to the northeast decreasing from 2000 mm to 250 mm (Gao 2004, Orodho 2006).

Topography, climatic conditions, soil types and human activity, all have a great impact on the vegetation types in Kenya. Three main types and several sub-types of Kenyan vegetation had been recognized by Edwards (1940): i) Forest types, subdividing into mountain forest, thorn forest, and mangrove forest; ii) Grasslands (including parkland or savannah grasslands), subdividing into mountain grassland, high moisture savannah, Acacia-tall grass savannah and open grassland (tall grass); iii) Semi-arid grasslands, subdividing into Acacia-desert grass savannah and open grassland (desert grass), and desert shrub-desert grass. In recent years, researchers from University of Copenhagen and The World Agroforestry Centre constructed the Potential Natural Vegetation of eight countries from eastern and southern Africa (VECEA team 2015).

The diverse vegetation types of Kenya include numerous indigenous plant species, many of which are endemic, such as Dendrosenecio keniensis (Asteraceae) in K4 (Mt. Kenya), Impatiens fischeri (Balsaminaceae) in K3 and K4, Habenaria keniensis (Orchidaceae) in K3, K4 and K5, and the recently published species Sedum keniense (Crassulaceae) in K4 (Mt. Kenya) (Zhou et al. 2016a). Over the years, botanists from all over the world have studied Kenyan plants and accumulated a series of monographs. In 1961, Dale I.R. and Greenway P.J. published "Kenya Trees and Shrubs", which recorded about 1000 trees and shrubs of Kenya (Dale and Greenway 1961), and Beentje H.J. republished this book in 1994 reviewing some species and adding lianas (Beentje 1994). In 1974, Agnew A.D.Q. published "Upland Kenya Wild Flowers" and republished it in 1994, recording over 3000 herbs and ferns of Kenyan upland areas; the third edition of which was published in 2013, with the addition of grasses and sedges (Agnew 1974, 2013, Agnew and Agnew 1994). Other books on Kenya plants include, "The wild flowers of Kenya" (Blundell, 1982), "An illustrated manual of Kenya Grasses"(Ibrahim and Kabuye 1987), "The beautiful plants of Kenya" (Karmali 1988), "Orchids of Kenya" (Stewart 2003), "Useful trees and shrubs for Kenya" (Maundu and Tengnas 2005), "Common plants of Kenya" (Wang et al. 2016), and some other books with a broader coverage of whole east Africa, such as "Collins guide to the wild flowers of East Africa" (Blundell 1987), "Field Guide to Acacias of East Africa" (Dharani 2006), "Medicinal Plants of East Africa, 3^rd Edition" (Kokwaro 2009), "Medicinal Plants of East Africa-An Illustrated Guide" (Dharani and Yenesew 2010), "Field Guide to Common Trees and Shrubs of East Africa, 2^nd Edition" (Dharani 2011). "Flora of Tropical Africa" was the first flora record of Kenya plants, which included 13000 plants of tropical Africa and divided into 10 volumes (Daniel et al. 1868–1933). "Flora of Tropical East Africa (FTEA)" covers plants from Uganda, Kenya and Tanzania, which has been edited several times since 1952 and completed in 2012. To date, FTEA records c.125000 plant species from the three countries. Shortcomings of FTEA on Kenya plants are that: i) taxa are still under-represented; ii) New families, genera and taxa have not been reviewed and recorded; iii) Families have not been arranged using the recent available botanical systems.

Plant systematics has been one of the hottest research areas in botanical studies (Singh 2010, Simpson 2010). In the early years, some plants systems were published based on morphological characteristics, such as Ching"s system on ferns (Ching 1978a, b), Cheng"s system about gymnosperms (Cheng and Fu 1978), and Takhtanjan"s system, Cronquist"s system and Engler"s system about angiosperms (Yang et al. 2004, Liu et al. 2015). Lycophytes had been separated from ferns according to recent molecular systematics evidences, and was positioned as the sister group to Euphyllophytes (including Spermatophytes and Monilophytes) (Pryer et al. 2004, Liu et al. 2009). Smith et al. (2006) proposed a new classification system on Monilophytes, dividing ferns into 4 classes, 10 orders and 37 families, and later some new families were established and new classification system was proposed (Christenhusz et al. 2011b, Liu et al. 2013, Zhang and Zhang 2015). Recently, the Pteridophyte Phylogeny Group proposed a community-derived classification on extant lycophytes and ferns, including 2 classes, 14 orders and 51 families (PPG I 2016). Based on branch taxonomy and molecular systematics results, the Angiosperm Phylogeny Group (APG) proposed a new classification, refined over four publications (APG 1998, APG II 2003, APG III 2009, APG IV 2016). Compared with the APG III system, the APG IV system proposed two additional informal major clades, namely superrosids and superasterids, and recognized 5 new orders, namely Boraginales, Dilleniales, Icacinales, Metteniusales and Vahliales, resulting in a total of 64 orders and 416 families of Angiosperms (APG IV 2016).

This article summarizes families and genera of Kenya plants based on FTEA, and combined with other recent molecular systematic research. Our goal was to answer the following questions: i) What is the total number of plant species found in Kenya? ii) Which families and genera are the largest? iii) Which part in Kenya contains the highest plant species richness, and iv) What measures can be carried out so as to protect and conserve the Kenyan plants?

All information is sourced from the FTEA, since it has recorded over 12500 vascular plants of Uganda (U1–U4), Kenya (K1–K7) and Tanzania (T1–T8), including some planted and naturalized species. Each family has been published in one volume, although some big families with 2–4 volumes also have been done, such as Leguminosae (4 volumes), Poaceae (3 volumes), Rubiaceae (3 volumes) and Compositae (3 volumes). Except for some exotic plants, FTEA has described each species, the distribution regions, and characteristic habitat. and recorded the voucher specimens.

Here, we conducted a census of all Kenyan species recorded by FTEA, gathering distribution information on endemic plants, exotic plants and naturalized species. We then reviewed the families and genera of all the species based on recent systematic research, creating a "Synoptic List of Families and Genera of Kenyan Vascular Plants (SLFGKVP)" (see Supplementary material 1). Families of Lycophytes and monilophytes are revised by PPG I system (PPG I 2016), families of gymnosperms are revised the system advocated by Christenhusz et al. (2011a), and families of angiosperms are revised by APG IV system (APG IV 2016). We analyzed the largest families and genera, as well as the number of endemic and exotic species of Kenya plants. We also compared total and endemic species number, and species density among different regions (K1–K7) of Kenya.

We would like to thank Juan Xie, Neng Wei, Yi Xue, Zhizhong Li and Zhun Xu from Wuhan Botanical Garden for their help on some statistical analysis of this article. We also thank Can Dai from School of Resources and Environmental Science, Hubei University, for improving the use of English in the manuscript. Thanks also due to P. de Lange, E. Farris and another anonymous reviewer for their valuable comments on the manuscript. This work was supported by Sino-Africa Joint Research Centre (Y323771W07 and SAJC201322) and National Natural Science Foundation of China (31361140360).