The clonal species probably originated from one or both of the other diploid species in the genus from Tasmania, L. tinctoria and L. polymorpha, through some kind of genetic mix-up during pollination and fertilization. This sometimes happens in plants: instead of one (haploid) set of chromosomes from each parent, producing an offspring with two sets, an offspring can receive one (haploid) set from one parent, plus two sets from the other (diploid), thus resulting in an individual with three sets (triploid). Such individuals are usually sterile in terms of sexual reproduction since they are unable to produce pollen/ovules with a normal chromosome number. However, if they can reproduce clonally they can persist indefinitely.
It doesn’t. While clones may persist for a time, they are unable to adapt to a changing environment nearly as fast as sexually reproducing organisms, putting them at a disadvantage. Most multicellular species that reproduce strictly by cloning are thought to be rather young. However, many species, like aspens, can reproduce both sexually and by cloning.
The ancestral species apparently were able to reproduce both sexually and by cloning.
There are quite a few species of lizards and amphibians that consist only of females and reproduce parthenogenetically, in other words , by cloning. Like these plants, many are tripliod crosses between two closely related parental species. These species mostly appear to be relatively young, suggesting that these clones don’t persist very long (order of tens of thousands of years, perhaps).