SUBCELLULAR STRUCTURES OF RELEVANCE TO THE ORIGIN OF LAND PLANTS (EMBRYOPHYTES) FROM GREEN-ALGAE

During the past 2 decades, a substantial body of structural, biochemical, and molecular evidence has been amassed in support of the hypothesis that charophycean green algae are the closest extant protist relatives of the land plants (embryophytes). Charophycean algae include the filamentous and unicellular Zygnematales, represented by the familiar Spirogyra and desmids; the relatively large and complex Charales, such as Chara; the less conspicuous, but well-studied Coleochaete; and several other less well-known taxa. Ultrastructural studies of these green algae have revealed a variety of subcellular structures which are shared with land plants, and which are absent from most other algae. This article describes the phylogenetic importance of the cytoskeleton (including mitotic and meiotic division apparatus), peroxisomes, cell wall features, and organelles found in specialized cells such as spermatozoids, by comparison with correlative subcellular structures in embryophytes.