Dicranema revolutum (C. Agardh) J. Agardh (1852 , p. 634)

Dicranema revolutum (C. Agardh) J. Agardh (1852, p. 634)

The generitype species is an obligate epiphyte of the seagrass Amphibolis antarctica (Labill.) Sond. & Asch. from subtropical Western Australia, eastward across temperate southern coasts to Victoria and south to Flinders I. in The Bass Strait ( Kraft and Womersley 1994). The thalli are erect, filiform and laxly to compactly dichotomous but not complanate ( Fig. 1 a View Fig ). Axes are composed of a narrow central core of compact filaments surrounded by a broad band of large hyaline, (sub-)isodiametric cells bounded by a thin compact cortex of small, pigmented cells ( Fig. 2 a View Fig ). Tetrasporangia occur subterminally in slightly swollen nemathecia at branch forks ( Fig. 3 a View Fig ) and are basally pit-connected to mother cells at the base of vertical cortical filaments ( Fig. 3 b View Fig ). At maturity the sporangia are immersed two or three cortical layers below surface cortical cells ( Fig. 3 b View Fig ). Spermatangia are catenate and form in scattered ampullar clusters deeply inset from the branch surface ( Fig. 3 c View Fig ). Gametophytes are monoecious, the cystocarps protuberant, ostiolate and single or in short series near branch apices ( Fig. 4 a, b View Fig ). Large cavities remain when outer pericarps and mature carposporophytes and carposporangia are shed ( Fig. 4 b View Fig ). Carpogonial branches are two-celled, the trichogynes smoothly cylindrical and arching toward the branch surface from deeply positioned supporting cells ( Fig. 4 c View Fig ). Presumably diploidised carpogonia appear to initially fuse at the bases of the trichogynes to apparently non-differentiated auxiliary cells situated within adjacent cortical filaments ( Fig. 4 d View Fig ), the auxiliary cells subsequently commencing to join with cells in neighbouring filaments to form elaborate fusion cells ( Fig. 4 e, f View Fig ) that issue numerous gonimoblast filaments in all directions ( Fig. 4 g View Fig ). A matrix of intermixed and secondarily pit-connected and fused cells of gonimoblast and vegetative filaments forms from the fusion cell and develops mostly toward the centre of the host axis ( Fig. 4 h View Fig ) whereas a cavity above the placenta opens up above the growing carposporophyte ( Fig. 4 i View Fig ). The leading surface consolidates with further growth of the mixed placental filaments and gives rise to a layer of free dendroid gonimoblasts ( Fig. 4 j View Fig ). Large obovoid to lachrymose terminal carposporangia subsequently cover the surface ( Fig. 4 k View Fig ) beneath the roof of the pericarp, where release is made through an ostiole on the side of the cystocarp opposite the diploidised auxiliary cell ( Kraft 1977 b, fig. 3c) or through the breakdown of the pericarp that begins at the ostiole ( Fig. 4 l View Fig ).