Studies of protonemal morphogenesis in mosses. X. Ephemeraceae revisited; new dimensions underground

Abstract

This systematic investigation of the filament systems in nine species of Ephemerum and two of Micromitrium revealed a range of new characters in the Ephemeraceae. Above ground most taxa have pointed chloronemata with widely spreading branches, whereas in Micromitrium, Ephemerum cohaerens and E. spinulosum, the branches are fastigiated. Four species of Ephemerum (E. sessile, E. cohaerens, E. spinulosum and E. hibernicum) have massive lipid-laden tubers, the last three with prominent spinulose side branches. Tubers, comprising chains of rounded cells, are described for the first time in Micromitrium. Unique to E. recurvifolium are starch-laden tubers and fragile chloronemal branches. The morphology of the diaspores reinforces the pottialean affinities of the Ephemeraceae. The production of long-lived tubers provides Ephemerum species predominantly found on lake and reservoir margins in the British Isles, with an alternative means of perennation on sites susceptible to inundation prior to sporophyte maturation.