I recently saw the NOVA program on the invasive algea C. taxifolia. (Altho originially tropical, it is thriving in the Mediterranian).
Anyhow, in both the show and one of the web sites it was mentioned that the plant is a single cell. How can that be? It seems WAY too big.
Also, it says that it can reproduce through fragmentation. If the fragment doesn’t have the nucleus, how can it do that (does the nucleaus split and one go with the fragment and one stay with the main plant?)
IIRC, some of these large ‘single celled’ organisms have many nuclei, just little or no internal membranes or walls, so they can’t really be called multicellular because, well, a cell is a cell - implying some form of containment.
Caulerpa taxifolia’s cytoplasm is multi-nuclear, so when a piece breaks off, it will contain not one, but thousands of copies of the plants genome. This coenocytic structure is not unique to C. taxifolia, but is also found in many slime molds.