![Sample our Environment & Agriculture journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5934/TOC-Subject-Sample-2021-Environment-Agriculture.jpg"})
ABSTRACT
The structure of canals in multiporate conceptacles of Mesophyllaceae is analysed and several distinct types are recognized. In what appears to be the plesiomorphic condition, canals are straight and bordered by non-differentiated pore cells. In the majority of Mesophyllaceae, pore cells are thinner-wider, starting from basal cells and extending towards the apical opening. This can be coupled with development of triangular (conical) or pyriform canals. Other modifications occur at species or genus level, or across several genera, the most distinctive being formation of cell bars (Phragmope discrepans), elongate basal cells (Melyvonnea), or branched pore filaments composed of fewer cells than adjacent roof filaments and provided with elongate subbasal (or basal and subbasal) cells (Thallis-Perithallis, respectively Printziana-Sunesonia). In Thallis-Perithallis-Sunesonia-Melyvonnea, pore filaments are composed of fewer cells than adjacent roof filaments and terminate below the roof surface. It is postulated that the elongate basal cells in Melyvonnea resulted after loss of basally branched pore cells, an evolutionary step that finds justification in the new genus Sunesonia where homologous cells become reduced or deteriorated. A new thallus organization (aniso-bilateral) characterized by a diminutive ventral perithallium distinguishes Perithallis. Nine new taxa are described, including accounts of their historical record, typifications, comparison of their types to new collections, and the published molecular work that provides further support: Thallis capensis gen. & sp. nov., Perithallis incisa gen. et comb. nov., P. chathamensis (Foslie) nov. comb., Printziana australis gen. & nom. nov. and Sunesonia pseuderubescens gen. et sp. nov.
Acknowledgements
Sincere thanks are due to Tommy Prestø (TRH), Jennifer Dalen (WELT), Joanna Wilbraham (BM), and William Woelkerling and Adele Harvey (LTB) for arranging the loans of collections to GB. Two reviewers and the subject editor, made comments on the manuscript.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 The same applies to the recently described ‘Crustaphytym’ (Liu et al. Citation2018, figures 3d, e, 4d–f) and ‘Tectolithon’ (Jesionek et al. Citation2020, p. 12, ‘no diagnostic morpho-anatomical features … observed’) in order to be validated (Art.44.2). These two putative new genera possess a combination of characters accommodated within the concept of Leptophytum (Athanasiadis and Adey Citation2006, p. 72) that includes species with ‘ … regular or rare patches of coaxial cells arranged in series of 2–15 arching rows’, ‘few branched (dendroid) SMCs, … centrally or in other places on the chamber floor’, and conceptacle overgrowth by peripheral filaments (Athanasiadis and Adey l.c., figures 105, 140) – even if the latter character is not evident in the generitype. Moreover, the postulation of ‘basal [pore] cells [in multiporate conceptacles of ‘Crustaphytym’] … smaller than the upper ones (figure 3g, h)’ (Liu et al. Citation2018, p. 3461) requires documentation, while ‘tetrasporangial conceptacle chambers relatively smaller (130–155 μm high by 115–200 μm wide)’ (Liu et al. Citation2018, p. 3467), have also been described in Leptophytum microsporum (Foslie) Athanasiadis and Adey (Citation2006, table 1, 70–110 × 110–220 µm). Current data suggest that specimens referred to ‘Crustaphytym’ and ‘Tectolithon’ display the plesiomorphic (non-differentiated) type of canals in multiporate conceptacles.