I am considering the evolution of plants, specifically considering the chloroplast. I am getting slightly confused and cannot seem to find the information I need to build a coherent picture in my head. Specifically, I have the following questions:
Is the defining feature of a plant cell that it has, or once had, chloroplasts? Is the group of plants all of the species which came from the single common ancestor eukaryotic cell which first acquired a photosynthesising bacterium as an endosymbiont?
In that case, the plants Alectoria sarmentosa (witch's hair lichen) and Monotropa uniflora (Indian Pipe), which are non-photosynthesising plants and do not have chlorophyll, must have some remanant of a chloroplast inside of them (unless they are not actually plants and are just plant-like fungi). My question here is, are these really plants? If so and it is true that plants are defined as all being descendant from this first photosynthesising eukaryote ancestor, then what is their 'remnant chloroplast'? I.e. what organelle do they have that used to be a chloroplast.
If it is true that there are plants which have organelles that used to be chloroplasts but not longer have chlorophyll and photosynthesise, then it is almost certainly the case that the chloroplasts carry out some function other than photosynthesis that is beneficial to the plant's survival (e.g. I know that remnant mitochondria- hydrogenosomes and mitosomes- are useful for fixing iron although they do not carry out respiration). What are the other functions of chloroplast-like organelles?