Algunos aspectos de la variabilidad de los oogonios en poblaciones actuales del género Chara (Charophyceae). Aplicación paleontológica

Abstract

A critical revision of some useful taxonomic criteria in paleontology of Charophytes is carried Out. The results are based in four modern populations ((Chara aculeolata, Chara aff.baltica, Chara delicatula and Chara globularis) and they permit to make some serious objections to these critera. The results are related with three principal aspects: the meaning of the absolute magnitudes of me girogonite, the behaviour of his joint variation and the morphological variability during the calcification process. In general, and for each one of the four populations, an absence of influence of the position of the girogonite over their measurements is observed. This doesn't happens when the verticil is considered as source of variation. These biometrical differences which are equivalent to some of those that has been used to distinguish fossil species, are not due to a process of progressive or heteregenous calcification in the secuence of verticils of me plant. Several arguments against the indiscriminate use of cocients between absolute magnitudes (e.g. the polarity index) as detectors of systematic interest are showed. In the same way, some remarks to the use of the morphology of the spiral calcificated cells, the prominence of the basal pore and some aspects of the apex shape, as taxonomic criteria are made. All this are variable within the same plant when there are differents in the calcification degree of the girogonites.