Experimental analysis of the life history of the complanate form of Scytosiphon (Scytosiphonaceae, Phaeophyta) in southern Australia

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Abstract
Scytosiphon which reproduces asexually and gives rise to similar blade-like plants was investigated. Analysis of the reproduction in culture of several strains of blades with different ancestries showed that blade-producing Scytosiphon arises parthenogenetically, developing directly from a small percentage (< 5%) of the gametes formed by gametophytic blades. In contrast, blades which arose from zooids, produced by either crustose sporophytes (derived from zygotes) or crustose plants with a parthenogenetic origin, were gametophytic and gave rise to crustose progeny. Culture conditions affected the reproduction of parthenogenetically-produced blades. Those derived from gametes formed in long days (12.5 h) produced crustose progeny. Those which originated in shorter days (9.5, 10.5 h) in some instances gave rise to blades, and this kind of asexual reproduction persisted for up to 4 successive generations. The roles of asexual and sexual processes in the life history of complanate Scytosiphon are discussed.