To determine which two species are the MOST closely related based on a cladogram, you typically look for the species that share the most recent common ancestor.
Without seeing the actual cladogram, I can provide some general guidance based on the relationships among these groups:
-
Spikemosses (Lycopodiophyta) and clubmosses (Lycopodiaceae) are both in the same broader category of vascular plants, specifically among the lycopods, so they are relatively closely related.
-
Flowering plants (Angiosperms) and ferns (Polypodiopsida) are also related, but they are separated by a significant evolutionary distance as ferns are non-flowering vascular plants.
-
Flowering plants and quillworts (Isoetes) are also distantly related, as they diverge from lycophytes before flowering plants evolved.
-
Clubmosses and ferns belong to different plant lineages (clubmosses are more primitive compared to ferns), making them less closely related.
Given this general information, if we assume typical relationships in plant evolution, the most closely related pair should be spikemosses and clubmosses (option a), as they are both part of the group of vascular plants known as lycophytes and share a more recent common ancestor compared to the other pairs.
Thus, the answer is: a spikemosses and clubmosses.