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Padina gymnospora is characterised by the thick thallus (up to 8 cell layers), the distribution of sporangia primarily on the superior surface of the thallus and the evanescent indusium. Specimens are collected in shallow pools in the sublittoral fringe (De Clerck et al 2002).
Thalli, attached by a small stupose rhizoidal base, are to 6.5 cm high, flabellate and composed of several lobes with inrolled margins. The superior surface (the side toward which the margin is inrolled) is slightly to moderately calcified. Thalli are olive-brown in colour. In transverse section the thallus is composed of 4-6 layers of cells in the mid-regions and up to 8-9 layers near the base. Hair rows are present on both sides of the thallus, but more conspicuous on the inferior side of the thallus. Tetrasporangia are arranged in concentric lines, above each hair row, mainly (but not exclusively) developed on the superior surface. An evanescent indusium is present but is usually only clearly visible in very young sori. Tetrasporangia are ovoid, up to 100 μm long and 70 μm wide. Gametophytes were not observed (De Clerck et al 2002).
De Clerck, O., H.R. Engledow, J.J. Bolton, J.J. Anderson and E. Coppejans 2002 Twenty marine benthic algae new to South Africa, with emphasis on the flora of Kwazulu-Natal. Botanica Marina 45:413-431.
Taken from Guiry, M.D. and G.M. Guiry 2009