Investigations of the taxonomy and morphological variation of Ulva (Chlorophyta): Ulva californica Wille

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Abstract
The taxonomic relationships of Ulva californica, U. angusta and U. scagelii were evaluated through morphological studies of field and herbarium specimens, and through culture studies. These species show ecological, morphological and cytological similarities but differ in size, habit and distributions. Morphological studies of specimens from Alaska to southern California indicate a gradation in size and habit with latitude. Thalli also vary predictably with wave energy and season. Laboratory studies indicate that isolates identified as U. californica and U. scagelii are capable of hybridizing and have similar developmental patterns. Both species can produce germination tubes and extensive basal rhizoidal discs. Development of the basal disc is influenced by temperature and other culture conditions. When grown at temperatures between 15° and 20°C the basal disc gives rise to numerous secondary thalli, resulting in a tufted habit. This compares well with field observations. Based upon morphological, cytological and developmental similarities, U. angusta and U. scagelii are placed as taxonomic synonyms under the older species, U. californica.

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