In biological classification , class ( Latin : classis ) is a taxonomic rank , as well as a taxonomic unit, a taxon , in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life , domain , kingdom , phylum , order , family , genus , and species , with class ranking between phylum and order.
7-505: Charophyceae is a class of charophyte green algae . AlgaeBase places it in division Charophyta. Extant (living) species are placed in a single order Charales , commonly known as "stoneworts" and "brittleworts". Fossil members of the class may be placed in separate orders, e.g. Sycidiales and Trochiliscales . Charophyceae is basal in the Phragmoplastophyta clade which contains the embryophytes (land plants). In 2018,
14-551: A distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct type of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in
21-424: A distinct rank of biological classification having its own distinctive name – and not just called a top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine
28-419: A taxonomy of the flowering plants up to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of
35-557: Is a single row of cortical cells the cortex is referred to as diplostichous , where there are two rows of cortical cells it is termed triplostichous . The intermodal cells elongate and do not divide, they become many times longer than broad. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data. Mesostigmatales Spirotaenia Chlorokybales Klebsormidiophyceae Charophyceae Coleochaetophyceae Zygnematophyceae Embryophytes (land plants) Class (biology) The class as
42-460: The animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed
49-568: The first nuclear genome sequence from a species belonging to the Charophyceae was published: that of Chara braunii . The thallus is erect with regular nodes and internodes. At each node there is a whorl of branches. The whole plant is calcified and Equisetum -like. The internodes of the main axis consist of a single elongated cell, in Chara the internodes are corticated covering the main axis. In other genera these are absent. Where there
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