On the Current Classification System of Paleozoic Seeds

Abstract

Abstract:

This paper summarizes the history of classifications of Paleozoic seeds and

revaluates the previous classification systems of Paleozoic detached seeds. The current status

of studies on Paleozoic. gymnosperms: has been deteched seeds and whole fossil

gymnosperms indicates that Seward’s classification system for Paleozoic seeds inadequate

since all the seeds of Cardiocarpales in his system are not cordaitean female reproductive or-

gans as Seward’s suggested. It is shown from investigations of whole fossil plants that the

members of Cardiocarpales were derived from at least three different major groups of

Paleozoic gymnosperms. Moreover, Meyen’s suggestion that the gymnosperms be classified

based on symmetry of seeds has been little supported since all the fossil gymnosperms have

not shown structurally preserved seeds and organic attachment.

In order to relate detached seeds to whole fossil gymnosperms, the present author sug-

gests that five families: Lagenostomaceae, Pachytestaceae, Callospermariaceae, Cryptospe-

rmaceae and Cardiocarpaceae be established for Paleozoic seeds and the Order

Trigonocarpales be renamed as Pachytestales since the genus Trigonocarpus does not now in-

clude structurally preserved seeds. Thus, the five families may be considered either as

subdivisions of the three orders of detached seeds: Lagenostomales, Pachytestales and

Cardiocarpales, or as female reproductive organs of whole fossil gymnosperms of the five

Permo-Carboniferous major groups: Lyginopteridales, Medullosales, Callistophytales

Gigantopteridales and Cordaitales.

A Key to Paleozoic seeds is provided as follows:

A. Seeds with a cupule; integument thin, simple, deeply lobed and less differe-

ntiated;nucellus united to integument up to the base of pollen chamber; pollen

chamber complex ................................. Lagenostomales, Lagenostomaceae

A. Seeds without a cupule; integument thick, complex, unlobed and differentiated into

several layers; nucellus free within integument except at the base; pollon chamber

simple ................................................................................................ B

B. Seeds radially symmetrical in shape; integumentary bundles present; nucellus bun-

dles typical ................................................... Pachytestales, Pachytestaceae

B. Seeds bilaterally symmetrical in shape; integumentary bundles present or absent;

nucellus bundles often untypical .................................... C (Cardiocarpales)

C. Bundles absent in integument; main bundle C-shaped in transverse section with

a sclerenchyma bundle ............................................ Cryptospermaceae

C. Bundles present in integument; main bundle not C-shaped in transverse section

without a sclerenchyma bundle ......................................................... D

D. Seeds very small with secretory cavities in integument; nucellus bundles limit-

ed in nucellus platform .......................................... Callospermariaceae

D. Seeds large without secretory cavities in integument; nucellus bundles limited

in nucellus platform or not ....................................... Cardiocarpaceae

Key words: Paleozoic, Detached seeds, Gymnosperms, New classification system, Phylogeny

Li Zhong-Ming. On the Current Classification System of Paleozoic Seeds[J]. .

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On the Current Classification System of Paleozoic Seeds

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