A palynological study of Heliophila (Brassicaceae) in southern Africa

Kumwenda, Mphamba Wayera (2003-04)

On t.p.: Systematics and Biodiversity Science.

Thesis (MSc)--Stellenbosch University, 2003.

Thesis

ENGLISH ABSTRACT: Pollen grains of the southern African genus Heliophila L. (Brassicaceae), were examined using light microscopy (77 taxa), scanning electron microscopy (82 taxa) and transmission electron microscopy (IOtaxa). The present study emanates from a pilot study by Kose (200 I) in which palynology was identified as one of the taxonomically informative data sources that can be used in the classification and subdivision of the genus Heliophila. The aim of this study was to assess the taxonomic significance of palynological data in the genus Heliophila. All pollen grains of Heliophila taxa are prolate in shape and tricolpate. The exine surface sculpture varies and two main groups are identified. In the majority of the taxa the sculpture is psilate or psilate micro-perforate with suprateetal spinules (Pollen Type A), whereas in the remaining taxa the sculpture is micro-reticulate to reticulate with or without suprateetal spinules (Pollen Type B). Pollen Type B may be divided further into three subgroups based on the shape of the lumina and the position of the suprateetal spinules. TEM results also confirm the two main groups as proposed by the SEM. The structural and sculptural features of the exine proved important in the demarcation of the pollen grains into two distinctively different pollen types and the other pollen morphological data such as pollen grain sizes, pollen grain shape are discussed in relation to the groups/subgroups of pollen types. The sculpturing types are discussed with regard to their evolution and pollination discussed with regard to plant habit and pollen size. Cluster analysis, based on vegetative and reproductive characters, excluding palynological characters, was performed only after the pollen types were identified. These groups were well supported by plant habit, life form, leaf type, presence or absence of appendages on the filaments, indumentum of filaments and presence of the stipe on the ovary and divided the genus Heliophila into two main clades. It was observed that this division followed a sim ilar pattern as the species arrangement in the classification by Marais (1970). AIthough the two main pollen types occur in both clusters proposed by the morphological analysis, the specific pollen types are restricted to distinct subclusters. In conclusion, pollen data reveals that Heliophila is a heterogeneous genus. The present study also reveals that it is difficult to subdivide the Heliophila taxa into infrageneric units on the basis of palynological evidence alone. In conjunction with other data sources, it does, however appear to have systematic significance. Therefore, the results of the present palynological study can be used as an additional source of evidence to support the subdivision of the Heliophila taxa into infrageneric units in the near future if a better understandinz and classification of the zenus is to b b be achieved.

AFRIKAANSE OPSOMMING: Stuifmeelkorrels van die suider Afrikaanse genus Heliophila L. (Brassicaceae) is met behulp van ligmikroskopie (77 taksons), skandeerelektronmikroskopie (82 taksons) en transmissie-elektronmikroskopie (IOtaksons) bestudeer. Die huidige studie is 'n uitvloeisel van 'n lootsprojek deur Kose (200 I) waarin palinologie geïdentifiseer is as een van die taksonomies-belangrike data-bronne wat in die klassifikasie en subdivisie van die genus Heliophila gebruik kan word. Die doel van die studie was om die taksonomiese waarde van palinologiese data van die genus Hettophila te bepaal. Alle stuifmeelkorrels van Heliophila taksons is prolaat in vorm en trikolpaat. Die oppervlak-skulptuur van die eksien varieer en twee hoofgroepe word onderskei. In die meerderheid van die taksons is die skulptuur psilaat of psilaat-mikroperforaat met supratektale uitsteeksels (stuifmeeltipe A), terwyl die skulptuur in die oorblywende taksons rnikro-retikulaat tot retikulaat met of sonder supratektale uitsteeksels (stuifmeeltipe B) is. Stuifmeeltipe B kan verder in drie subgroepe, gebaseer op die vorm van die lumens en die posisie van die supratektale uitsteeksels, verdeel word. Resultate verkry vanaf die TEM bevestig die twee hoofgroepe soos voorgestel deur die SEM-studies. Die strukturele en skulpturele kenmerke van die eksien blyk belangrik te wees in die verdeling van die stuifmeelstruktuur in twee duidelike stuifmeeltipes en ander morfologiese kenmerke, byvoorbeeld die grootte en vorm van die stuifmeelkorrels word bespreek in hul verhouding tot die groepe / subgroepe van die stuifmeeltipes. Die tipes stuifmeel-skulptuur word bespreek ten opsigte van hul evolusie en bestuiwing word bespreek ten opsigte van groeiwyse en stuifmeelgroottes. Groepanalise, gebaseer op vegetatiewe en reproduktiewe kenmerke, uitsluitend palinologiese kenmerke, is saamgestel nadat die stuifmeeltipes geïdentifiseer is. Die groepe word gevorm op grond van groeiwyse, groeivorm, blaartipe, aan- of afwesigheid van aanhangsels aan die helmdrade, die indumentum van die helmdrade en die aanwesigheid van 'n stipe op die vrugbeginsel en verdeel die genus Heliophila in twee hoofgroepe. Daar is waargeneem dat hierdie analise 'n soortgelyke patroon volg as die spesie-rangskikking in die klassifikasie van Marais (1970). Alhoewel die twee stuifmeeltipes in beide die morfologiese hoofgroepe aanwesig is, stem die stuifmeeltipes duidelike ooreen met die sub-groepe wat deur die morfologiese analise gevorm is. Ten slotte, stuifmeeldata dui daarop dat Heliophila 'n heterogene genus is. Die huidige studie dui ook daarop dat' n onderverdeling van Heliophila in infrageneriese eenhede op grond van palinologiese kenmerke alleen ook baie moeilik is, maar saam met ander kenmerke kan stuifmeeldata wel van taksonomiese waarde wees. Dus, die resultate van hierdie studie kan as 'n aanvullende bron van data gebruik word om 'n onderverdeling van die genus te steun en 'n klassifikasie van die genus daar te stel.

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