Are All Paraphyllia the Same?

Ulyana N Spirina,Michael S Ignatov,Tatiana V Voronkova

doi:10.3389/fpls.2020.00858

Abstract

Moss paraphyllia, the trichome-like or foliose structures on moss stem surfaces, are usually treated as epidermal outgrowths. However, in some taxa of the moss families Leskeaceae, Neckeraceae, and Amblystegiaceae their distribution along the stem is consistently correlated with parts of the stem surface near branch primordia. In other moss families, Climaciaceae, Hylocomiaceae, and Pseudoleskeaceae the specific paraphyllia-generating epidermal layer produces paraphyllia evenly all along the stem. These results suggest that there are at least two different types of regulation of paraphyllia development; however, both of them may be involved in the morphogenesis of paraphyllia in some families, for example in the Thuidiaceae. Exogenous abscisic acid treatment consistently increases the number of paraphyllia of the Leskea-type, and it also induces the development of proximal branch leaves that normally do not develop a lamina above the stem surface. This fact supports conclusions regarding the homology of the Leskea-type of paraphyllia with leaves.

Highlights

IntroductionTheir morphology remains incompletely understood despite a long history of studies
Mosses are small plants, and their morphology remains incompletely understood despite a long history of studies
Distribution of Paraphyllia Along the Stem The evaluation of the distribution of paraphyllia along the stem was performed quantitatively using zones associated with the morphogenesis of branch primordia (Figures 3A, B)

Summary

Introduction

Their morphology remains incompletely understood despite a long history of studies. Among the most controversially interpreted features are foliose and filamentose appendages on the stem surface in pleurocarpous mosses, commonly called paraphyllia and pseudoparaphyllia. An interest in their structure has been recently revived after molecular phylogenetic studies showed that many morphological characters used in “classical taxonomy” are enormously homoplasious and can no longer be used as key diagnostic characters. Previously neglected features of branch primordia, and the arrangement of foliose structures around branch initials, appear stable enough to serve as diagnostic characters for family-level classification (Ignatov, 1999) The terminology of these structures and interpretation of their homology, remain incongruent, as different manuals sometimes refer to the same cases in conflicting ways

Methods

Results

Conclusion