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dc.contributor.advisorVan der Schijff, H. P.
dc.contributor.authorRobbertse, Petrus Johannes
dc.date.accessioned2018-01-12T06:14:21Z
dc.date.available2018-01-12T06:14:21Z
dc.date.issued1971-07
dc.identifier.urihttp://hdl.handle.net/11660/7582
dc.description.abstractEnglish: The genus Acacia is an extensive one with representatives in Africa, America, Asia and Australia. When Bentham revised the subfamily Mimosoideae in 1875 he divided the taxon into six subgenera. All the South African representatives of the genus were placed in the two subgenera Vulgares and Gummiferae. Bentham distinguished between the two subgenera by the differences in morphology of the stipules. Bentham's classification of the subgenera differs from that of Oliver (1871), whose grouping of the South African Acacia species is based on the morphology of the inflorescence. Species which are affected by this difference are A.albida, A.schweinfurthii and A.kraussiana. Because of this problem and the fact that, judging from the literature, there is some uncertainty regarding the application of taxonomic criteria, it is necessary that the whole genus be revised. Due to the extent of such a project it was decided to limit this investigation to the South African species with the main emphasis on characters which could be of taxonomic importance. Where it was deemed necessary a few species from other geographical areas were included in the investigation. Various characters were found which were valuable for considerations of phylozenetic history of the genus and for delimitation of taxa. On the basis of the presence of starch grains in the cotyledons and the morphology of the seedlings, A.albida, A.kraussiana and A.schweinfurthii were placed in a new subgenus, Farinosae. On the basis of these characters the subgenus Farinosae shows affinity with the subgenera Phyllodinae, Bothryocephalae and Pulchellae of Australia and certain Vulgares species of America. The subgenus Farinosae can possibly be phylogenetically regarded as the oldest extant taxon of the genus Acacia. With the species A.albida, A.krau8siana and A.schweinfurthii in a separate subgenus, the remaining South African members of the subgenera Vulgares and Gummiferae can be separated on the basis of classical features such as the morphology of the stipules and inflorescences. Other clear differences which were found between these two subgenera are as follows: (a)The flower of the Vulgares (and Farinosae) species contains a cup-like disc to which the filaments are adnate, and the ovary has a prominent pedicel (gynophore). In the flower of the Gummiferae species the disc is lacking and the ovary is almost sessile. A disc and pedicelled ovary are also found in the flower of A.albida and the name Feidherbia albida which Chevalier proposed for this taxon in 1934 is therefore not justified. The origin of the cup-like disc on which the stamens are found can probably be regarded as a relict of an ancient branched system on which stamens were borne and which later became reduced. (b) In the pods of the Vulgares (and Farinosae) species the fibre zone consists of both cross and longtitudinally arranged fibres, while the pods of the Gummiferae species have only longtitudinally arranged fibres, or none at all. (c) In the pinnules of the Vulgares (and Farinosae) species a few layers of spongy parenchymatous cells are found between the abaxial and adaxial palisade parenchyma cells. In the pinnules of the Gummiferae species the abaxial and adaxial palisade cells are continuous. (d) The seedlings of the Vulgares species have membranous or leaf-like stipules while the stipules of the Gummiferae species are spinescent. Hooked spines are absent on the Gummiferae seedlings but appear on the Vulgares seedlings either dispersed on the internodes or arranged in groups of two or three directly below the nodes. On the basis of the morphology of the flower, the anatomy of the pod and the morphology of the seedlings, the Vulgares and Gummiferae species can be divided into smaller groups and, in certain cases, into definite species. Keys have been compiled to facilitate the classification. Interesting differences between the Vulgares and Gummiferae species were noted with regard to the nocturnal movements of the leaves. These differences were, however, not very clear in all cases. In the case of certain species such as A.polyacantha and A.robusta the nocturnal movements are very conspicuous and specific (see Fig. 125). A hypothesis was postulated concerning the evolution of the inflorescence systems and inflorescences of the genus Acacia. The hypothesis includes a theory concerning the development of the involucel (cupula). Flowering dates of the different Acacia species are determined to a large extent by the morphology of the inflorescence system. Date of flowering can therefore be considered as a genetic character which nevertheless can be influenced to a certain extent by ecological conditions. The development of the ovule and the ontogeny of the seed was investigated. Ideas were put forward as to the possible homology of the ovule. A study of seed ontogeny produced information concerning the presence of endosperm in mature seeds of A.kirkii, A.tortilis and A.xanthophloea. This characteristic cannot be used as a criterium to remove these three species, as well as other exotic species containing endosperm in the seed, out of the genus Acacia (cf. Vassal, 1968). The arrangement of vascular tissue in the seedling, leaves and young shoots are discussed. Judging from the arrangement of the primary vascular bundles in the seedling there is probably a relationship between a monolacunar node with two leaf traces, a trilacunar node and a node which is called the "fifth type" by Takhtajan (1969). It may be concluded that the extant South African taxa of the genus Acacia can be distinguished from each other on a specific level. By using variable characters such as degree of pubescence and numerical taxonomic characters such as seed and leaf size it is possible to carry the subdivision of species too far. It is therefore recommended that the taxa with an extensive distribution, manifesting considerable variation, such as A.karroo Hayne, A.caffra Willd., A.reficiena Wawra (= A.luederitzii Engl.) and A.robusta Burch., should not be divided into smaller taxa until more information is available concerning the abovementioned characteristics. As a final summary, a key has been composed in which as many characters as possible have been used to distinguish between the South African Acacia species.en_ZA
dc.description.abstractAfrikaans: Die genus Acacia is 'n groot genus met verteenwoordigers in Afrika, Amerika, Asië en Austraiië. Bentham het met sy hersiening van die subfamilie Mimosoideae in 1875 die takson in ses subgenera verdeel. Volgens Bentham se indeling ressorteer al die Suid-Afrikaanse verteenwoordigers van die genus onder die twee subgenera Vulgares en Gummiferae. Bentham het die twee Suid-Afrikaanse subgenera van mekaar onderskei op grond van die uitbeelding van die steunblare. Wanneer Bentham se indeling van die subgenera vergelyk word met Oliver (1871) se groepering van die Suid-Afrikaanse Acacia-spesies, wat gebaseer is op die uitbeelding van die bloeiwyse, salopgemerk word dat die omgrensing van die twee indelings verskil. Soorte wat by die verskil betrokke is, is A.albida, A.schweinfurthii en A.kraussiana. Met bogenoemde probleem in gedagte en die feit dat dit uit die literatuur blyk dat daar heelwat onduidelikheid bestaan oor die toepassing van taksonomiese kriteria by die omgrensing van taksa, is dit nodig om die hele genus te hersien. Weens die omvang van so 'n werk is daar met hierdie ondersoek slegs op die Suid- Afrikaanse soorte gekonsentreer, en die klem het geval op moontlike taksonomiesbelangrike eienskappe. Waar nodig is enkele soorte uit ander geografiese gebiede ook ondersoek. Verskillende eienskappe is gevind wat toegepas kan word om meer lig te werp op die moontlike filogenetiese geskiedenis van die genus en ook op die omgrensing van taksa. Op grond van die aanwesigheid van setmeel in die saadlobbe en die morfologie van die kiemplante is A.albida. A.kraussiana en A.schweinfurthii in 'n nuwe subgenus, naamlik die Farinosae geplaas. Op basis van genoemde eienskappe skakel die subgenus Farinosae met die subgenera Phyllodiaae, Bothryocephalae en Pulchellae van Australië en sekere Vulgares-soorte van Amerika. Die subgenus Farinosae kan moontlik filogeneties as die oudste bestaande takson van die genus Acacia beskou word. Na die verwydering van die taksa, A.albida, A.kraussiana en A.schweinfurthii, kan die Suid-Afrikaanse verteenwoordigers van die subgenera Vulgares en Gummi-ferae volledig van mekaar onderskei word op grond van die klassieke kenmerke, naamlik die uitbeelding van die bloeiwyse en steunblare. Ander konkrete verskille wat tussen die twee subgenera gevind is, is die volgende: (a) In die blom van die Vulgares-soorte (en Farinosae-soorte) word 'n kelkvormige skyf aangetref waaraan die meeldrade vergroei is en die vrugbeginsel besit 'n duidelike steel (ginofoor). By die Gummiferae-soorte ontbreek die skyf en die vrugbeginsel is feitlik sittend. 'n Skyf en 'n gesteelde vrugbeginsel word ook in die blom van A.albida aangetref en daarom is die naam Feidherbia albida wat Chevalier in 1934 vir hierdie takson voorgestel het, ongegrond. Die oorsprong van die kelkvormige skyf waarop die meeldrade voorkom, kan moontlik nog 'n oorblyfsel wees van In eens vertakte sisteem waarop meeldrade gedra was, maar wat later gereduseer is. (b) By die peule van die VUlgares-soorte (en Farinosae-soorte) bestaan die veselsone uit dwars- en lengteverlopende vesels, terwyl dit by peule van die Gummiferae-soorte slegs uit lengteverlopende vesels bestaan of ontbreek. (c) By die pinnulas van die Vulgares-soorte (en Farinosae-soorte) kom daar tussen die abaksiale en adaksiale palissade-parenohiemselle, In paar lae sponsparenohiemselle voor. By die pinnulas van die Gummiferae-soorte is die abaksiale en adaksiale palissade-parenchiemselle aaneenlopend. (d) Die kiemplante van die Vulgares-soorte het membraanagtige of blaaragtige steunblare, terwyl die steunblare van die Gummiferae-soorte doringagtig is. Haakdorings ontbreek by die Gummiferae-kiemplante, maar word by die Vulgareskiemplante verspreid op die internodia, of in groepe van twee of 2 drie net onder die nodia gedra. Op grond van die morfologie van die blom, die anatomie van die peul en die morfologie van die kiemplant kan die Vulgares- en Gummiferae-soorte in kleiner groepies ingedeel en in sekere gevalle tot op spesifieke vlak onderskei word. Sleutels is opgestel om hierdie indeling te vergemaklik. Interessante verskille tussen die Vulgares- en Gummiferae-soorte is ook opgemerk by die slaapbewegins wat deur die blare uitgevoer word. Hierdie verskille is egter nie altyd baie duidelik nie. By sekere spesies soos A.polya-cantha en A.robusta is die slaapbewegings egter baie opvallend en spesifiek (sien Fig. 125). In Hipotese is opgesteloor die moontlike evolusie van die bloeisisteme en bloeiwyses van die genus Acacia. In die hipotese kom ook In teorie oor die totstandkoming van die omwindseltjie skutblare voor. Die blomtyd van die verskillende Acacia-soorte word in In groot mate bepaal deur die morfologie van die bloeisisteem. Blomtyd kan daarom gesien word as In genetiese eienskap wat wel in 'n mate deur ekologiese toestande beïnvloed kan word. Die ontwikkeling van die saadknop en die ontogenese van die saad is nagegaan. Gedagtes is gewisseloor die moontlike homologie van die saadknop. Die ontogenie van die saad is ook nagegaan om inligting in te win oor die aanwesigheid van endosperm in die volwasse saad van A.kirkii. A.tortilis en A.xantho-phloea. Hierdie eienskap kan nie as In kriterium gebruik word om bogenoemde drie spesies en ander uitheemse spesies waar endosperm in die saad voorkom, uit die genus Acacia te verwyder nie (vgl. Vassal, 1968). Die verloop van die vaatweefsels in die kiemplant, blare en jong stingels word bespreek. Volgens die verloop van die primêre vaatbondels in die kiemplant kan daar 'n moontlike verband gesien word tussen In monolakunêre knoop met twee blaarspore, In trilakunêre knoop en In knoop wat deur Takhtajan die "fifth type" genoem word. Daar word tot die gevolgtrekking gekom dat die bestaande Suid-Afrikaanse taksa van die genus Acacia tot op spesifieke vlak duidelik van mekaar onderskei kan word. Deur van variërende kenmerke soos graad van beharing en nummeriestaksonomiese kenmerke soos saadgrootte en groottes van die blaar gebruik te maak kan daar moontlik te ver gegaan word met die onderverdeling van spesies. Dit word dus aanbeveel dat die taksa met In wye verspreiding, waar aansienlike variasie voorkom, soos A.karroo Hayne, A.caffra Willd., A.reficiens Wawra (= A.luederitzii Engl.) en A.robusta Burch., nie in kleiner taksa verdeel behoort te word, voordat meer gegewens ingewin is oor bogenoemde eienskappe nie. As finale samevatting word In sleutelopgestel waarin daar van soveel eienskappe as moontlik gebruik gemaak word om die Suid-Afrikaanse Acaciaspesies van mekaar te onderskei.af
dc.description.sponsorshipW.N.N.R.en_ZA
dc.language.isoafaf
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectAcacia -- Morphologyen_ZA
dc.subjectAcacia -- South Africaen_ZA
dc.subjectThesis (D.SC. (Plant Sciences))--University Free State, 1971en_ZA
dc.title'n Morfologiese studie van die genus Acacia Miller in Suid-Afrikaaf
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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