Phylogeny and Ontogeny of Charophyta: ABSTRACT

Abstract

The oldest known occurrence of the Charophyta is from the Devonian of eastern Europe. Devonian and Lower Mississippian rocks also contain the most diverse types of charophytes but their pre-Devonian ancestors are still unknown. During the Devonian the dextrally spiralled forms of the Trochiliscaceae increased in size, the number of spiral units decreased, and calcium carbonate was first secreted in coronula cells. Some workers believe that the reticulate forms of the Sycidiaceae and vertically ribbed forms of the Chovanellaceae are related closely and represent utricula. In the Middle Pennsylvanian through middle Permian are found the sinistrally spiralled forms with apical pores and hollow spirals of Stomochara Grambast. Palaeochura Bell has six spirals and is the only post-Devonian form of that type with the exception of some modern types. The upper Permian and Triassic contain forms not End_Page 526------------------------------ fundamentally unlike their Pennsylvanian ancestors. The apical pore, which was probably the germination point, was retained. Beginning in Late Jurassic and continuing through the Recent, conditions were more favorable throughout the world for charophyte growth and many different forms evolved. The utricle coverings of the gyrogonite, apical rosettes, peripheral groves, thinned apical areas, basal structures, nodes, and variations in structure of the spiral units evolved as their abundance apparently increased and ecologic niches became more abundant and varied. The ontogeny of the Tertiary forms also reflects this change. There is some enigma about the modern types because they are not as diverse as one might expect with the modern geologic setting of high continents and abundance of fresh- and brackish-water environments. Large collections containing many variations of growth stages are of greatest importance in the study of phylogenetic and ontogenetic characters. Because of this, selection of types commonly is misleading in taxonomic studies of the Charophyta. End_of_Article - Last_Page 527------------