Ignatov, M.S., U.N. Spirina, M.A. Kolesnikova, D.A. Ashikhmina, E.A. Ignatova & S.V. Polevova. Peristome development pattern in Encalypta poses a problem: what is the primary peristomial layer in mosses?

Arctoa (2018) 27: 1–17

doi: 10.15298/arctoa.27.1

Peristome development was studied in mosses of the subclass Funariidae: Encalypta procera, E. longicolla, E. rhaptocarpa, E. vulgaris, Timmia bavarica and Funaria arctica. Peristome of Encalyptaceae is characterized by thick inner peristomial layer (IPL), so up to the late stages of its development its cells do not divide, maintaining basic peristomial formula 4:2:2 (omitting preperistomial layers). No regular offsetting is seen, and cells in all amphithecial layers are aligned by their anticlinal cell walls. Further development to the stage of 4:2:4 may proceed very late, so the formula 4:2:2 may remain in mature peristomes. Moreover, occasional anticlinal divisions occur in primary peristomial layer (PPL), so one IPL cell sometimes adjoins to two cells in the PPL. Such anticlinal divisions in PPL are also observed in Timmia, though we failed to find them in Funaria. The revealed additional divisions in PPL pose a question on its definition. Original criteria for PPL recognition given by Blomquist & Robertson (1941) are discussed and found contradicting the pattern in Encalypta in a number of important aspects. In all studied species of Encalypta the IPL seems to keep a development regulatory functions, which are a characteristics of PPL in peristomes of most arthrodontous mosses. This developmental pattern of peristome in Encalypta may explain an extraordinal diversity of peristomes in this genus, varying from 5-layered to simple and then to totally reduced. Neglected aspects of the peristome development in Funaria are also discussed.