Thesis: Contribution to the biosystematics of Celtis L. (Celtidaceae) with special emphasis on the African species.
Celtis L. (Celtidaceae, earlier part of the Ulmaceae) is a genus mainly of tree species, which has its natural distribution in Africa, the Mediterranean region, Asia, North and South America, and northern Australia. Outside this natural distribution various species are planted in temperate areas, but they occur in many different ecological habitats, tropical and temperate regions in all continents. Some species are ornamental; some are used for timber and reforestation.
This thesis is focused on African Celtis with general objectives such as providing a phylogeny of the Celtidaceae, understanding the relationships of African Celtis, preparation of a revision of the African Celtis species, a study of the main morphological characters, and a conspectus containing all names and synonyms in the genus. This thesis provided results, such as: Ulmaceae s.l. is not monophyletic and we confirm that this family has to be split into two families, Ulmaceae s.s. and Celtidaceae; the Celtidaceae should merge with Cannabaceae; in general Celtis is monophyletic but for more support we need to add more markers and taxa. In the relationships of Celtis, a few clades can be seen especially for South American species, which have thorns and by this morphological character that clade is distinguished from the rest of the genus Celtis. African and Asian Celtis form a mixed clade, this clade could have been influenced by the dispersal of these species. In total 12 African Celtis are identified in Africa and Madagascar: Celtis adolfi-friderici, C. africana, C. australis, C. mildbraedii, C. gomphophylla, C. prantlii, C. tessmannii, C. toka, C. wightii, and C. zenkeri. On Madagascar there are two endemic species: C. bifida and the newly described species Celtis malagasica. For Australia a new species was separated from the “Celtis philippensis complex”: Celtis australiensis. The main morphological characters in African Celtis instrumental for the distinction of species include leaf shape, venation, indumentum, stomata, inflorescences, flowers, pollen, fruits and their endocarps. Two pollen types could be distinguished based on the feature of the apertures, also two types of hairs are distinguished (glandular and non-glandular); stomata include three types: paracytic, cyclocytic and anisocytic; inflorescences are cymose and fruit shape are drupes, the endocarp of Celtis differs from globose ellipsoid to ovoid with different sizes, colours, and texture.The conspectus contains about 500 names of specific and infraspecific rank, many of which remain to be verified to complete publication and typification details. Generally for getting better relationship patterns of this genus revision of the Asian Celtis is recommended.