Life histories ofAcrosymphyton firmumandSchmitzia evanescens(Rhodophyta, Gigartinales): Carpospore germination and development

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Abstract
Acrosymphyton firmum Hawkes and Schmitzia evanescens Hawkes are confirmed as having heteromorphic life histories, with both taxa having a diminutive crustose phase as the alternate stage. In S. evanescens gametophytes developed directly from the crust without formation of tetrasporangia. In the absence of cytological information two hypotheses are proposed to explain this life history pattern. One hypothesis invokes lack of sexual reproduction and parthenogenetic development of the carposporophyte, whereas the other hypothesis invokes sexual reproduction with somatic, instead of tetrasporic, meiosis. Possible effects of somatic versus tetrasporic meiosis on potential genetic diversity in the population needs to be examined. The life history of A. firmum was not completed in laboratory culture and requires further investigation. The gametophytes of both species are spring annuals which inhabit cobble substrata in the subtidal zone. The alternate crustose phases are abrasion resistant and thus enable these taxa to persist on an unstable, seasonally disturbed (by winter storms) substratum.

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