Primary module acrocarpous

In Rhizogonium and Pyrrhobryum Section Pyrrhobryum, innovations on the perichaetial modules form new perichaetial modules (Figure 14.5B), but not vegetative primary modules (discussed further in Chapter 3). The placement of these taxa in the pleurocarpous mosses, in a basal grade containing several acrocarpous taxa (BeU and Newton, 2005, see also Chapter 3), could indicate that the presence of subperichaetial innovations in these taxa is a retained plesiomorphic condition, whereas in taxa such as Amblystegium this condition is an independently derived reversal. 

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