To determine which two species are the most closely related based on a cladogram, you would typically look for the species that share the most recent common ancestor (the closest branching point on the cladogram).
In the context of the groups you listed:
- Flowering plants
- Ferns
- Clubmosses
- Spikemosses
- Quillworts
Without seeing the actual cladogram, we can't definitively state which two groups are closest. However, if we assume a typical evolutionary relationship among these plant groups:
- Flowering plants (angiosperms) are generally more closely related to ferns, as they share a more recent common ancestor compared to the clubmosses and spikemosses.
- Clubmosses (lycophytes) and spikemosses are typically nested within the same clade as they are both lycophytes but may not be as closely related as flowering plants to ferns.
- Quillworts are also a type of lycophyte but can be more distantly related to other groups given they represent more distinct evolution.
Based on the evolutionary tree of these plants, the most common interpretation is that flowering plants and ferns could likely be concluded to be the most closely related.
So the answer is: a flowering plants and ferns.