Browsing by Author "Chuba, David"

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    A comparative study of the distribution of C₃ and C₄ species of Cyperaceae in South Africa in relation to climate
    (1999) Chuba, David; Stock, William D
    In this study the contribution of the climatic factors such as temperature, altitude, and mean annual precipitation as well as phylogeny to the determination of the distribution of C₃ and C₄ genera of Cyperaceae in South Africa has been investigated. Multiple regression analysis was used to determine the climatic factor that best predicted percent C₄ distribution. To see if the C₄ syndrome was influenced by taxonomy, the percentages of C₄ species was determined for each of the subtribes and genera. The results show that the relationship between the climatic factors and percentage of C₄ Cyperaceae species is similar to what has been found for the grasses (Vogel et al., 1978). However C₃ species of Cyperaceae seem to be abundant in most parts of South Africa. Only minimum growing season temperature showed significant correlation (P = 0.000391) with percentage C₄. The presence of the C₄ syndrome is shown to have some consistency within subfamilies, tribes and genera.
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    The phylogeny of Brachycorythis Lindl. and Neobolusia Schltr
    (1999) Chuba, David; Linder, H Peter
    The monophyly of the genus Brachycorythis has been tested. The phylogeny of the African genera of Orchidinae - Orchideae - Orchidaceae (Schwartzkopffia, Brachycorythis, Neobolusia, Schizochilus, Dracomonticola, Holothrix and Bartholina is estimated with special attention to phylogenetic positions of Brachycorythis and Neobolusia. Pollen surfaces of twelve of the species are examined. Thirty-eight morphological and anatomical characters for 25 species of the species mentioned above are cladistically analysed and the stability of the different clades of the most parsimonious trees determined using various clade stability indices. The current delimitation of the Southern African Orchidae genera, with Neobolusia and all the other genera being independent from Brachycorythis is supported. Pollen surface ornamentation also shows the only species of Neobolusia examined for this (N. tysonii) as being quite different from the rest of the genera studied in having intectate pollen whereas the rest have semitectate pollen. This has further indicated support for the independence of Neobolusia from the genus Brachycorythis.