Ultrastructure and development of sporoderm in Andreaeobryum macrosporum Steere & BM Murray (Andreaeobryopsida)

Sporoderm development in Andreaeobryum is studied and confirned to be similar to that in Andreaea in having no lamellate structure in the exine. The formation of the outer layers of the spore wall, external to the intine, proceeds by the accumulation of sporopollenin granules originating within the special wall of the sporocyte. Despite the outermost sublayer having a pattern similar to the perine in most mosses, and consequently was earlier reported as perine, it is mostly formed before the initial sporocyte walls disappear, thus questioning significant tapetal contribution. Therefore, we suggest to referring the outer sporoderm layer of Andreaeobryum to exine, whith has however is not originated by means of the tripartite lamellae, as in ferns, lycopods, hornworts, liverworts, and all other mosses excepting Andreaeobryopsida and Andreaeopsida. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The sporoderm development in Andreaeobryum is similar to Andreaea in lacking a lamellate structure. The outer layers of the spore wall are formed by the accumulation of sporopollenin granules originating within the sporocyte's special wall. The outermost sublayer, previously called perine, is mostly formed before the initial sporocyte walls disappear, questioning the tapetal contribution.