The phylogenetic and potential functional significance of leaf anatomical and physiological traits of southern African Oxalis

Jooste, Michelle (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The southern African Oxalis radiation is extremely morphologically variable and few characters are known as synapomorphies supporting DNA-based clades, hindering species identification, taxonomic revision and understanding of functional trait evolution in this clade. Sixty-eight leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades. This study showed that the combination of six leaflet anatomical traits (stomatal position, adaxial epidermal cell types, abaxial epidermal cell types, mesophyll type, sheath around vascular tissue and degree of leaflet conduplication) clearly support various clades de ned by previous DNA-based phylogenetic work. Despite the phylogenetic patterns detected in the aforementioned traits, other leaflet anatomical traits were highly variable and showed no phylogenetic pattern: these traits could possibly hold functional significance. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region (GCFR) and provide a basis for future hypotheses regarding its radiation. Limited previous work on Oxalis has shown evidence for CAM photosynthesis in some South American species and preliminary anatomical work on southern African Oxalis hinted at Kranz anatomy, typically associated with C4 photosynthesis. We assessed stable carbon-isotope data, stomatal conductance and anatomical traits for 67 southern African Oxalis species to test whether any indigenous species show alternative modes of photosynthesis. All assessed taxa followed an exclusively C3 photosynthetic pathway. The measured stomatal conductance data of southern African Oxalis species showed that many species make minimal effort to prevent water loss, even though Oxalis was previously regarded as a water-conservative genus (Kluge and Ting (1978); Proches et al. (2006a); Biocyclopedia: Oxalis (2012)). Additionally we observed that the majority of southern African Oxalis species have epistomatic leaflets, which is regarded as the rarest stomatal position among all angiosperms. Interestingly, epistomatic leaflets had significantly smaller stomata (which enables fast response to changes in environmental conditions) and significantly higher conductance rates (which enables carbon fixation to take place at a faster rate). We propose that this strategy would be favoured under the strongly seasonal environment in which the majority of southern Africa Oxalis grows (winter rainfall Mediterranean climate), as this enables these plants to take advantage of their growing conditions to ensure high productivity, rapid growth and successful carbon storage into their below-ground organs. We propose that the strategy of small adaxially-located stomata with high conductance rates might be an overlooked key innovation driving diversification into one of the largest geophytic plant lineages within the GCFR.

AFRIKAANSE OPSOMMING: Die suider-Afrikaanse Oxalis radiasie is morfologies geweldig variërend, en min kenmerke is bekend as sinapomorfies wat DNA-gebaseerde klades ondersteun, wat spesie-identifikasie, taksonomiese hersiening en 'n begrip van funksionele kenmerk evolusie in hierdie klade bemoeilik. Agt-en-sestig blaartjie anatomiese kenmerke van 109 suider Afrikaanse Oxalis spesies is ondersoek op soek na filogeneties beduidende kenmerke wat klades afbaken. Die studie het aangedui dat die kombinasie van ses blaartjie-anatomiese kenmerke (stomata posisie, adaksiale epidermale sel-tipes, abaksiale epidermale sel-tipes, mesofil sel-tipe, skede rondom vaatweefsel en graad van blaartjie toevouing) verskeie klades wat deur vroeëre DNA-gebaseerde filogenetiese werk gedefinieer is, ondersteun. Ten spyte van die filogenetiese patrone waargeneem in hierdie kenmerke, was ander blaartjie anatomiese kenmerke hoogs variërend en het min filogenetiese patrone gewys: hierdie kenmerke mag funksioneel betekenisvol wees. Die inligting wat in hierdie studie vergader is sal die taksonomiese hersiening van hierdie spesie-ryke lid van die Groter Kaapse Floristiese Streek (GKFS) steun en 'n basis daarstel vir toekomstige hipoteses ten opsigte van sy radiasie. Beperkte vroeëre werk op Oxalis het bewys gelewer vir CAM fotosintese in sommige Suid-Amerikaanse spesies en voorlopige anatomiese werk op suider-Afrikaanse Oxalis het Kranz anatomie, wat tipies met C4 fotosintese geassosieer word, gesuggereer. Ons het stabiele stikstof-isotoop data, stomata geleiding en anatomiese kenmerke van 67 suider-Afrikaanse Oxalis spesies ondersoek om te toets of enige inheemse spesies van alternatiewe tipes fotosintese gebruik maak. Alle taksa wat ondersoek is maak uitsluitlik van C3 fotosintese gebruik. Die stomata geleidingsdata wat gemeet is was hoër as wat verwag is. Hierdie inligting het die wyse waarna hierdie genus gekyk word omgekeer, siende dat Oxalis vroeër as water-konserwatief beskou is, maar hierdie data dui aan dat baie Oxalis spesies minimale pogings aanwend om water te bespaar. Addisioneel het ons waargeneem dat die meerderheid suider-Afrikaanse spesies epistomatiese blaartjies het, wat beskou word as die skaarste stomata posisie binne die angiosperme. Interessant genoeg, het epistomatiese blaartjies beduidend kleiner stomata (wat vinnige reaksie op veranderinge in omgewingskondisies moontlik maak) en beduidend hoër geleidingstempos (wat dit moontlik maak vir stikstof fiksering om teen 'n vinniger tempo plaas te vind). Ons stel voor dat hierdie strategie verkies sou word onder die sterk seisoenale omgewing waarin die meeste suider-Afrikaanse Oxalis spesies groei (winter reënval Mediterreense klimaat), aangesien dit hierdie plante in staat stel om voordeel te trek uit hulle groei-omstandighede en hoë produktiwiteit, vinnige groeitempo en suksesvolle stikstofstoring in hulle ondergrondse organe verseker. Ons stel voor dat die strategie van klein, adaksiaal-geplaasde stomata met hoë geleidingstempos 'n onopgemerkte sleutel innovasie mag wees wat die diversifikasie tot een van die grootste geofietise plant-ontwikkelingslyne in die GKFS mag dryf.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98423
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