Introduction
Grasses of West and North sub-Sahara Africa - The flora of the grasses of WNSA deals with all the grasses of the African region stretching from the southern Sahara to the Atlantic Ocean and to North East, East and Central Africa, an area of 11.823 million km2 of which about half is desert.
Currently the Grasses of NWSA include 866 species in 186 genera. Almost half of the African grasses exists in the WNSA-area. Sosef (2017) reports 1885 grass species in 268 genera for the whole of Africa. The NWSA-flora is based on literature, own observations, the Brahms database, studies of herbaria collections and the records from the Paris MNFM-database. The species treatment includes taxonomic information, regional literature, a description, a distribution map, drawings and photographs. Extensive use has been made of the Flora of West Tropical Africa (1972), Flora of Ethiopia, Flora of Tropical East Africa (1970-1982), the online Plant List and Kew Grasses Database, and the Genera Graminum by Clayton and Renvoize (1986) during the preparation of this Flora. A complete overview of all the species with an initial treatment will be available as soon as possible. Eventually all available information from collections will be included in the Brahms database. The species of 5 bamboo genera that are introduced from Asia and tropical America and only cultivated in experimental bamboo gardens are only recorded in this work.
The flora will not provide taxonomic treatments of grass taxons but give comprehensive descriptions of the taxa based on the current knowledge. At the moment, with the advanced DNA-technology and knowledge the taxonomic understanding of the grass family increases dramatically. Many well-known genera like Pennisetum and Brachiaria are included in other genera and for the near future it is expected that more of the current understanding of the taxons will change. The advantage of an on-line publication is the possiility to include new understandings directly into the flora.
The collections of the WNSA grasses are found mainly in many European and regional herbaria as well as in. Important herbaria are Kew (Anglophone countries), Paris (Francophone countries), Missouri, Brussels, Wageningen, Lisbon and Coimbra (Cape Verde and Guinea Bissau), Berlin (Togo) and Missouri.
The grasses of WNSA will eventually be available in two languages, initially in English and on the longer term the French version will be added. Grass experts and students, especially those from the African region, are invited to collaborate in the Grasses of WNSA. That could be through contributions of tribes or genera. Interested contributors can contact me (tonvanderzon@gmail.com).
Available:
Oryzeae (keys, species descriptions, figures) 16 species
Aristideae (keys, species descriptions, figures, distribution maps) 32 species
Arundinelleae (keys, species descriptions, figures) 37 species
Andropogoneae (keys, species description) 217 species
Classification
Grasses form an important family of plants. The family is spread over all continents and often form an important or dominant element of the vegetation. The African steppes and savannahs are characterised and often dominated by tall grasses generally with the C4 photosynthesis, an adaptation to a warm and dry environment. A number of authors still work on the general classification of the grasses. I follow the work of Kellogg 2015 and of Soreng & al. 2015 who divide the grasses in 12 subfamilies and 51 tribes. I however include the Paspaleae in the Paniceae, following Sosef, 1997 and Hörandl & Stuessy, 2010.
Family Gramineae Juss. (1789) or Poacae Barnhart (1895) (alternative valid names)
I- Subfamily Pharoideae
1 Tribe Phareae: Leptaspis
II- Subfamily Puelioideae
2 Tribe Atractocarpeae: Puelia
3 Tribe Guaduelleae: Guaduella
III- Subfamily Oryzoideae
4 Tribe Streptogyneae: Streptogyna
5 Tribe Ehrharteae: Ehrharta
6 Tribe Oryzeae: Leersia, Maltebrunia, Oryza, Suddia
IV- Subfamily Bambusoideae
7 Tribe Arundinarieae: Phyllostachys, Yushania
8 Tribe Olyreae: Olyra
9 Tribe Bambuseae: Bambusa, Dendrocalamus, Gigantochloa, Guadua, Oxytenanthera, Pseudoxythenanthera
V- Subfamily Pooideae
10 Tribe Stipeae: Piptatherum, Stipa, Stipellula
11 Tribe Brylkinieae: Koordersiochloa
12 Tribe Brachypodieae: Brachypodium
13 Tribe Poeae: Agrostis, Aira, Avena, Calamogrostis, Castellia, Cutandia, Dactylis, Deschampsia, Festuca, Gastridium, Hypseochloa, Koeleria, Lachnagrostis, Lamarckia, Lolium, Phalaris, Poa, Polypogon, Pseudobromus, Rostraria, Trisetopsis, Vulpia
14 Tribe Bromeae: Bromus
15 Tribe Triticeae: Hordeum, Triticum
VI- Subfamily Aristidoideae
16 Tribe Aristideae: Aristida, Stipagrostis
VII- Subfamily Panicoideae
17 Tribe Thysanolaeneae: Thysanolaena
Tribe Centotheceae: Centotheca, Megastachya
18 Tribe Tristachyideae: Danthoniopsis, Dilophotriche, Loudetia, Loudetiopsis, Trichopteryx, Tristachya
19 Tribe Gynerieae: Gynerium
20 Tribe Paniceae (incl. Paspaleae): Acritochaete, Acroceras, Adenochloa, Alloteropsis, Anthephora, Axonopus, Cenchrus (incl. Pennisetum), Cyrtococcum, Digitaria, Echinochloa, Entolasia, Eriochloa, Ichnanthus, Louisiella, Melinis, Microcalamus, Oplismenus, Ottochloa, Panicum, Paratheria, Paspalum, Poecilostachys, Pseudoechinolaena, Sacciolepis, Setaria (incl. Paspalidium), Snowdenia, Steinchisma, Stenotaphrum, Trichantecium, Tricholaena, Thyridachne, Urochloa (incl. Brachiaria)
21 Tribe Arundinelleae: Arundinella
22 Tribe Andropogoneae: Anadelphia, Andropogon, Arthraxon, Bothriochloa, Capillipedium, Chasmopodium, Chrysopogon, Cleistachne, Coix, Cymbopogon, Dichantium, Diectonis, Diheteropogon, Elionurus, Elymandra, Eremopogon, Eriochrysis, Euclasta, Exotheca, Hackelochloa, Hemarthria, Heteropogon, Hyparrhenia, Hyperthelia, Imperata, Ischaemum, Lasiurus, Loxodera, Microstegium, Monocymbium, Ophiurus, Oxyrhachys, Parahyparrhenia, Phacelurus, Polytrias, Rhytachne, Rottboellia, Saccharum, Schizachyrium, Sehima, Sorghastrum, Sorghum (incl. Cleistachne), Thelepogon, Themeda, Trachypogon, Tripsacum, Urelytrum, Vossia, Zea
VIII- Subfamily Arundinoideae
23 Tribe Molinieae: Crinipes, Elytrophorus, Phragmites
IX- Subfamily Micrairoideae
24 Tribe Isachneae: Coelachne, Heteranthoecia, Isachne
X- Subfamily Danthonioideae
25 Tribe Danthonieae: Pentameris, Phoenanthoecium, Schismus
XI- Subfamily Chloridoideae
26 Tribe Centropodieae: Centropodia
27 Tribe Triraphideae: Habrochloa, Triraphis
28 Tribe Eragrostideae: Enneapogon, Eragrostis (incl. Harpachne, Pogonarthria), Schmidtia
29 Tribe Zoysieae: Sporobolus (incl. Crypsis, Spartina), Urochondra, Zoysia
30 Tribe Cynodonteae: Acrachne, Aeluropus, Bewsia, Chloris, Chrysochloa, Coelachyrum, Ctenium, Cynodon (incl. Brachyachne), Dactyloctenium, Desmostachya, Dinebra, Diplachne, Disakisperma, Eleusine, Enteropogon, Eustachys, Halopyrum, Leptocarydion, Leptochloa, Leptothrium, Lintonia, Melanocenchris, Microchloa, Ochthochloa, Oropetium, Perotis, Schoenefeldia, Tetrapogon, Tragus, Trichoneura, Trigonochloa, Tripogon
(In italics the introduced genera and genera recently included in other genera.)
Topography and Geography
The WNSA-region extends from Cape Verde and Mauritania through Senegal, Gambia, Guinea Bissau, Guinea, Sierra Leone, Liberia, Mali, Ivory Coast, Burkina Faso, Ghana, Togo, Benin, Niger, Nigeria, Cameroon, Tsjaad, Central African Republic, Sudan and South Sudan, 22 countries following the southern part of the Sahara. It is bounded by the Western Sahara, the Mediterranean North Africa (Morocco, Algeria, Tunisia, Libya and Egypt) , the Red Sea, North East Africa (Eritrea and Ethiopia), East Africa (Uganda and Kenya) and Central Africa (DR Congo, RP Congo, Gabon, Equatorial Guinea).
The ecoregions include the Sahara desert region, the Sahel steppe region, the Sudanian savannah region, and the Upper Guinean, Lower Guinean and Congo forest regions, each with their specific grasses. In the North the grass vegetation is closely related to the Mediterranean vegetation, in the South the grass vegetation of southern Cameroon and CAR has close links with the forest grasses of Central Africa and in the east the grass vegetation of CAR, Sudan and South Sudan is related to the vegetation of Somalia, Ethiopia and East Africa. Throughout the WNTA there are mountain ranges with their specific grass vegetation, the interrupted mountain belt of West Africa from Fouta Djallon, Mt Loma (1950 m), Mt Tingi,Mt Ziama, Mt Nimba and the lower Akwapin, Atewa Mt and Togo highlands, the Nigeria-Cameroon mountains including the Adamawa plateau, culminating in Mt Cameroon (4100 m) and in the Eastern Sahara the Aïr, Tibesti and Jebel Marra (3071 m) highlands. These grasses are related to the temperate grasses of Europe and Asia but also to the grasses of the mountains of East Africa.
The WNSA-region has about 125 endemic grass species, 14.5 % of the total number. Important centres of endemism are the mountains of Guinea/Liberia/Ivory Coast, the mountains of Nigeria/Cameroon and the savannahs of RCA and Southern Sudan.
Uses
Grasses are a very important plant family for mankind. The cereals form the main composing element of the human food with rice, maize, wheat, sorghum and teff and a couple of minor cereals. The grasses of the pastures provide the feed for the cattle and sheep and goat but also for the wildlife. Grasses are also used for roofing and for the walls of traditional houses and there are quite a lot of traditional pharmacopoeial uses known. These uses are included in the species descriptions.
Grass literature for the region
The most comprehensive overview of the grasses of WNSA is provided by Clayton in the Flora of West Tropical Africa (1972), dealing with the western part of the WNTA-region from Cape Verde to the western Cameroon. No comprehenisive overview exists for the eastern part of the WNSA-region. For most of the individual countries more recent treatments of the grasses have been elaborated, sometimes as a checklist but others very comprehensive. Scholz and Scholz elaborated the grasses of Togo (1983), Poilecot did the elaboration for Ivory Coast (1995) and Niger (1999), Van der Zon for Cameroon (1992) and Ghana (2017, in print) and Akoègninou et al. for Benin (1996). Checklists were made for Burkina Faso (Thiombiana et al., 2012), Cape Verde (Gomez, 1995), Chad (Lebrun, 1970), Guinea (Lisowski, 2009), Guinea Bissau (Catarino et al., 2006), Mali (Boudet et al., 1986), Mauritania (Barry, 1990, Lebrun, 1995), Niger (Peyre de Fabregas & Lebrun, 1976), RCA (Boulvert, 1977), Sahara (Ozenda, 1983), Senegal (Lebrun, 1973), Sudan and South Sudan ( Darbyshire, 2015).
For most of the surrounding countries of Mediterranean North Africa (Morocco, Algeria, Tunisia, Lybia, Egypt), Ethiopia and Eritrea, East Africa (Uganda, Kenya), Gabon and Equatorial Guinea comprehensive publications on the grasses are availbale. For the Central African grasses (DRC, Rwanda and Burundi) currently an extensive study is underway.
Morphology of the grasses
Gramineae are annual or perennial herbs, or tall woody bamboos.
Flowering stems (culms) are jointed, internodes hollow or solid; branches arising singly from nodes and subtended by a leaf sheath. Leaves are arranged alternately in 2 ranks and differentiated into sheath, blade, and an adaxial erect appendage or row of hairs or just a mere discoloration at sheath/blade junction (the ligule); the sheath surrounds and supports the culm-internode; the blades (“leaves”) are divergent, usually long, narrow and flat, but varying from inrolled and filiform to ovate with parallel veins, sometimes with cross-connecting veinlets.
The inflorescence is terminal or axillary, an open, contracted, or spike like panicle, or composed of lax to spike like racemes that are arranged along an elongate central axis or digitate, paired, or occasionally solitary; axillary inflorescences are often subtended by spatheoles (specialized bladeless leaf sheaths) and gathered into a leafy compound panicle; spikelets are often aggregated into complex clusters in bamboos. The central axis of the raceme (rhachis) is usually tough, sometimes fragile and breaking into internodes.
Spikelets are composed of distichous bracts or bracteoles arranged along a slender axis (rachilla); typically the 2 lowest bracteoles (glumes) subtend 1 to many florets. Florets are composed of 2 opposing bracts enclosing a single small flower, the outer bract (lemma) clasps the more delicate, usually 2-keeled inner bract (palea); the base of floret often has a thickened prolongation articulated with the rachilla (callus); at least the upper lemma often has an apical or dorsal bristle (awn), glumes also are sometimes awned. The florets are bisexual or unisexual with 3 stamens, rarely 1, 2, 6, or more in some bamboos, hypogynous, filaments capillary, anthers versatile; ovary 1-celled, styles (1 or)2(rarely 3), free or united at base, topped by feathery stigmas, exerted from sides or apex of floret. Fruits normally are dry indehiscent caryopses with thin pericarp firmly adherent to seed; the pericarp is rarely free, fleshy in some bamboos; the embryo small or large and the hilum punctate to linear.
Acknowledgments
My gratitude is for the herbarium-staff of the herbaria of Leiden/Wageningen, Kew, Paris, Lisboa and Coimbra for supporting and guiding me in their collections , for the collegues Jan Wieringa and Maarten van 't Zelfde for their support of elaborating the flora with the descriptions and maps, the Naturalis staff for helping me with the Linnaeus-programma, for the Senckenberg Gesellschaft for Naturforschung for allowing me to use the figures of Poilecot's Les Poacées de Côte d'Ivoire et les Poaceae de Niger and the Plantentuin Meise for using the plates of the unpublished Flore Illustrée du Sénégal, tome X. The work is being supported financially by the Hugo de Vries Fonds.
Leiden, Dr. Ton (A.P.M.) van der Zon