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Phylogenetic Relationships of the Zosterophylls and Lycopsids: Evidence from Morphology, Paleoecology, and Cladistic Methods of Inference

Patricia G. Gensel
Annals of the Missouri Botanical Garden
Vol. 79, No. 3 (1992), pp. 450-473
DOI: 10.2307/2399750
Stable URL: http://www.jstor.org/stable/2399750
Page Count: 24
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Phylogenetic Relationships of the Zosterophylls and Lycopsids: Evidence from Morphology, Paleoecology, and Cladistic Methods of Inference
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Abstract

Zosterophylls have been considered the probable ancestors of lycopsids since the establishment of the group in 1968 by Banks. Both share the characters of exarch protosteles and reniform sporangia, and it is argued that characters separating the two, e.g., microphylls and leaf-associated sporangia, could easily be derived by modification of zosterophyll emergences and sporangial position. Recently, different opinions concerning the derivation of lycopsid features have been proposed and an earlier time of occurrence of lycopsids has been suggested. The purpose of this paper is to evaluate the position of zosterophylls relative to lycopsids employing current information and considering prevailing theories. Aspects of morphology and ecology of zosterophylls and lycopsids are summarized, various evolutionary theories are evaluated, and a preliminary phylogenetic analysis involving zosterophylls, lycopsids, and selected other types of early land plants is presented. The cladograms suggest that zosterophylls and lycopsids are monophyletic based on the characters employed in the study. However, critical information is lacking that would allow a more precise estimate of affinity among all early land plants and between zosterophylls and lycopsids. Determining homologies is difficult, and early land plants exhibit extensive homoplasy.

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