Tylotus obtusatus (Sond.) J. Agardh (1876 , p. 428)

Tylotus obtusatus (Sond.) J. Agardh (1876, p. 428)

Thalli of this variably contoured species are recorded from Champion Bay (Geraldton), Western Australia, to Inverloch , Victoria ( Kraft and Womersley 1994, p. 330). The thalli are typically darkly pigmented, almost black and coarsely foliose, smooth margined, basically dichotomous and erect or repent from prostrate basal portions ( Fig. 1 i View Fig ) anchored by scattered stout haptera ( Fig. 7 a View Fig ). Some thalli are shades of mahogany brown, especially when tetrasporangial ( Fig. 1 j View Fig ). Thalli are ‘cellular’ (pseudoparenchymatous) throughout, derived from a broad cluster of marginal initials ( Fig. 2 f View Fig ), the interior cells of mature axes becoming compact and thick-walled ( Fig. 2 g View Fig ). Tetrasporangia form in elongate nemathecia ( Fig. 1 j View Fig ) and grow on and among lengthy palisade filaments, the sporangia mostly flush with the surface but with scattered others, possibly non-functional, occurring at the bases or subsurface along the lengths of the filaments ( Fig. 3 l View Fig ). Male ampullae are borne on subsurface mother cells and form tight clusters of two-celled spermatangial filaments ( Fig. 3 m View Fig ). Cystocarps form on dorsal surfaces of fronds ( Fig. 7 a View Fig ) and produce three-celled carpogonial branches at various depths in the cortex, the carpogonia lying in proximity to the supporting cell ( Fig. 7 b View Fig ), and borne on basal and hypogynous cells that partially wrap around what will become the auxiliary cell ( Fig. 7 c, d View Fig ). There is direct evidence of procarpy in that the presumably diploidised carpogonium clearly fuses with the supporting cell ( Fig. 7 d View Fig , arrow) and that this fusion precedes the formation of a compact fusion cell. Subsequent gonimoblast growth is lateral from the fusion cell ( Fig. 7 f View Fig ) and spreads across a basal, presumably nutritive, layer of gametophytic cells as the ostiole differentiates and a cavity opens beneath the thick pericarp ( Fig. 7 g, h View Fig ). The fusion cell persists throughout extensive carposporophyte growth in which gonimoblast and host gametophyte interconnections appear to occur mostly or only along the carposporophyte base ( Fig. 7 i, j View Fig ) rather than in a placental mixture. The leading surface of the carposporophyte begins to invaginate with maturity ( Fig. 7 j, k View Fig ), producing increased surfaces on which gullies and pockets ( Fig. 7 l View Fig ) are lined with short filaments with terminal spherical carposporangia ( Fig. 7 m View Fig ) .