Exostome reduced

Besides frequently having orthotropous capsules, epiphytic pleurocarps possess several other sporophytic character states more often than species of other habitats. These include short setae, ovoid to cylindrical and straight capsules, round stomatal pores, lack of or a poorly developed separating annulus, rostrate lids, papillose lower exostome outer surface, reduced exostome primary... 

Previous studies on variation in peristome morphology include an intergeneric snrvey of endostome variation in 70 species of diplolepidous mosses (Shaw and Rohrer, 1984), and stndies of Bryaceae (Shaw, 1985) and Brachytheciaceae (Ignatov et al., 1998). The infraspecific variation in the exostome ornamentation in the reduced peristome of Pterigynandrum flliforme had resulted in a number of varieties being described (Buck, 1980). 

The exostome is formed from the common periclinal cell wall pair between the inner wall of the OPL and the outer wall of the PPL. The endostome is formed from the common periclinal cell wall pair between the inner wall of the PPL and the outer wall of the IPL (Figure 12.1). Autolysis of the anticlinal walls of the cells between the exostome and the endostome separates the two rings of the diplolepidous peristome, while autolysis of the periclinal walls between adjacent teeth separates the structures within each ring of the peristome. In reduced peristomes this autolysis may be incomplete, leaving adjacent structures partially attached. 

Interpretation of the range of ornamental patterns found within the family as currently recognized is also problematic. Are these ancestral states that predate the evolution of reduction Given the complexity of the internal anatomy of the striate and papillose exostomes, it is tempting to consider these as ancestral. The alternative hypothesis that the peristome evolved the reduced state and concurrently or subsequently evolved these different ornamental patterns together with the marked internal differentiation seems contradictory. 

Exostomes well developed (0) or reduced (1). The length of the exostome teeth was used to estimate the degree of exostome reduction. Taxa with exostome teeth up to 350 J,m long were coded as rednced. 

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