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A Classification of Plants into Higher Taxa Based on Cytological and Biochemical Criteria

Peter Edwards
Taxon
Vol. 25, No. 5/6 (Nov., 1976), pp. 529-542
DOI: 10.2307/1220106
Stable URL: http://www.jstor.org/stable/1220106
Page Count: 14
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A Classification of Plants into Higher Taxa Based on Cytological and Biochemical Criteria
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Abstract

A variety of schemes are employed currently for the classification of plants into higher taxa. The two most widely used schemes, the traditional kingdom Plantae with sub-kingdoms Thallophyta and Embryophyta, and the Whittaker five-kingdom system with plants in the kingdoms Monera, Protista, Fungi and Plantae, rely on nineteenth century morphological criteria for delimitation of taxa that result in polyphyletic assemblages of organisms. It is proposed that plants be assigned to seven kingdoms, subordinate to the superkingdoms Procaryota and Eucaryota which are based on the procaryotic and eucaryotic types of cellular organization. The distribution of accessory chlorophylls is used as a major taxonomic criterion for classifying photosynthetic organisms at the kingdom level. This results in a single kingdom, the Cyanochlorobionta for photosynthetic plants containing chlorophyll a only within the superkingdom Procaryota. Photosynthetic plants within the superkingdom Eucaryota have been divided into three groups, the kingdom Erythrobionta for organisms with no accessory chlorophyll or occasionally chlorophyll d (and lacking flagella), the kingdom Chlorobionta for organisms with accessory chlorophyll b, and the Ochrobionta for those organisms with accessory chlorophyll c. Vascular plants have been assigned to a single division, the Tracheophyta, since in addition to having a similar biochemistry (chlorophylls a and b, similar carotenoids, starch as a reserve food product) they possess also a basic morphological groundplan -- a vascular system containing xylem and phloem, and a life history consisting of an alternation of generations. The fungi have been assigned three kingdoms as opposed to most extant schemes of classification in which they are allocated to a single polyphyletic assemblage. The true fungi have been divided into kingdoms Fungi 1 and Fungi 2 since it is thought that they have evolved from the Chlorobionta and Ochrobionta, respectively; the myxomycetes have been placed in a third kingdom, the Myxobionta.

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