North American Primitive Paleozoic Charophytes and Descendents

Abstract

North American primitive Paleozoic charophytes consist of three orders: Chovanellales (proposed herein), Sycidiales, and Trochiliscales, disposed in three families (Chovanellaceae, Sycidiaceae, and Trochiliscaceae) and three genera, Chovanella, Sycidium, and Moellerina with seven species generically allocated as follows: Chovanella (1), Moellerina (4), and Sycidium (2). The fourth, and evolutionarily advanced order of charophytes, Charales, is represented in the Paleozoic by the sinistrally spiralled Middle Devonian Eochara (Family Eocharaceae) which gave rise to the Pennsylvanian Palaeochara (Palaeocharaceae) which subsequently gave rise to the Stellatocharaceae, new family, the ancestral stock of the clavatoraceids, and through the clavatoraceids to the lagynophoraceids. The porocharaceids, also derived from Eochara, are the stem from which the Mesozoic and Cenozoic charoideid and nitelloideid charophytes evolved.

A new family, Stellatocharaceae, is proposed to include those genera previously placed in the subfamily Stellatocharoideae (nonutricled, but with apical beak). The gyrogonite of Catihlochara Peck and Eyer, 1963 has heretofore been inverted, and it is herein considered to be a junior synonym of Stomochara Grambast, 1961. Stomochara is placed in the family Porocharaceae, for not only is the apical pole of Stomochara different from that of Stellatochara Horn of Rantzien, 1954, but also the shapes of the gyrogonites and the geologic ranges of the two genera are different: Stomochara ranged from the Pennsylvanian to Triassic, but Stellatochara is a Mesozoic form known from the Triassic.

A fundamental dichotomy of the porocharaceid stock into nitelloideids (with a double tier of crown cells) and charoideids (chareids) (with a single tier of crown cells) occurred in the Late Jurassic and both groups became co-dominant in the Quaternary. The raskyellaceids (Late Cretaceous-Late Oligocene) branched from the chareid stock in the Late Cretaceous; these forms close their large apical pore by means of an apical operculum (surrounded by a circular dihescent suture). The gyrogonids (with peripheral modifications and nodose ornamentation of the apical zones) branch from the chareid stock in the Early Paleocene and persisted until the Late Oligocene. The chareid characeans persist until the present day, and are probably represented in the Late Eocene by Chara (or Charites, the organ genus in which the gyrogonite is indistinguishable from Chara). In the chareids there is progressive diminution (and finally essential disappearance) of the apical opening.

The scheme of orientation of the gyrogonites presented by Conkin, et al. (1970, 1972, and 1974) is consistent with the orientation of oogonia of modern charophytes and has resulted in the suppression of Karpinskya (Croft, 1952) Grambast, 1962, the correct orientation of Devonian and/or Mississippian Moellerina, Chovanella, and Sycidium, as well as a number of Pennsylvanian, Permian, and Mesozoic genera, and clarification of evolution within the charophytes. An evolutionary lineage within the genus Moellerina Ulrich, 1886, emend. Conkin, et al., 1974, based on progressive prominence of the cage superstructure, permits recognition of charophyte zones within the Middle and Upper Devonian and Lower Mississippian. Further, the usefulness of Moellerina greenei for precise age determination and correlation within the Middle Devonian of eastern North America is demonstrated.