Cape Town – Over the past 15 million years South Africa’s common wood sorrel has developed an arsenal of the most unique and extreme germination strategies in Cape flora.
Yet the same strategies that have allowed the delicate plants to grow and survive in the most uninhabitable places, like the Richtersveld, Knersvlakte, Oorlogskloof and Gifberg, may now be to its detriment under a fast- changing climate.
In a study published in the American Journal of Botany, Dr Michelle Jooste from the Department of Botany and Zoology at Stellenbosch University describes a continuum of germination states for 64 species of Oxalis, from germinating within 24 hours to lying dormant for several years, while waiting for the ideal environmental conditions.
Professor Léanne Dreyer, one of the co-authors and a leading expert on southern African Oxalis, said the wood sorrel’s germination strategies were nothing short of weird, extreme and unique in the plant kingdom.
“Oxalis had to adapt to a Mediterranean climate, subjected to long hot and dry summers alternating with a very predictable wet winter rainfall season. Dealing with these two extremes, which have remained stable for the past 15 million years, enabled Oxalis to take germination strategies to a whole new level,” Dreyer said.
More unusual is the incidence of inverse germination in some Oxalis species, where the seed leaves and first foliar leaf develop rapidly and appear to sustain rapid growth of the seedling before the root hairs emerge.
“This is a remarkable phenomenon, and it’s happening at the speed of light, as the plant needs to have enough time and produce sufficient resources within a single growing season to also form a bulb in order to survive underground during the hot, dry summer months,” Dreyer said.
The researchers noticed that some of the recalcitrant species produce large amounts of a thick gluey substance, called mucilage, upon germination.
They are now investigating the presence of bacteria in the mucilage, which appear to be symbiotically associated with the seeds - symbiosis is when two or more organisms live together in a mutually beneficial association.
Even more extreme are those Oxalis species of which the seeds are capable of either rapid germination or staying dormant.
“These seeds have the benefit of immediate germination if environmental conditions are favourable, or to delay germination until conditions become more favourable,” Dreyer said.
These types of seeds are extremely rare, and in the case of Oxalis, only 19% of the 64 species studied - selected to be as representative as possible of the nearly 230 known southern African Oxalis species - displayed intermediate germination.
Intermediate and recalcitrant species (56%) are almost exclusively restricted to the winter rainfall areas of the Cape, while orthodox species (24%) are present in both summer and winter rainfall areas.
Dreyer said they regarded the orthodox strategy as the ancestral state among Oxalis species.
The big question is whether Oxalis has one more survival strategy in its arsenal, to deal with drier conditions and a less predictable winter rainfall in the Cape Floristic Region as predicted by models of future climate change.
“If not, we stand to lose more than 50% of Cape Oxalis species - that’s more than 115 species,” Dreyer said.