1.5 Methods of Study
9
The diversity in size and sculpture of spores found within one and the same
sporangia was confirmed by the studies of Eggert and Taylor (1966): “The spores
exhibit a remarkable diversity in size and ornamentation ranging from smoothwalled immature forms to mature, highly ornamented types”. The variation within
one species in Eggert and Taylor’s study shows similarities to the fossil spores
of Raistrickia and Apiculatisporites on one hand, and to Punctatisporites and
Calamospora on the other hand.
Lindstrom et al. (1997) examined and studied pollen extracted from single
complete Glossopterid sporangia and found an enormous variation in the pollen
morphology.
The problem with the present intricate classification (e.g. Potonie) in use for
fossil dispersed spores and pollen was discussed and summed up by Balbach (1966)
as follows: “Although current systems of plant microfossil classification are usable
stratigraphically, the lack of a botanical taxonomic basis has led to the naming of a
multiplicity of species, many of doubtful biological validity. There should be no reason
why a botanically valid classification may not be made usable stratigraphically and
vice versa”.
Indeed, recent studies of spores and pollen isolated from fossil sporangia and
pollen sacs attached to fossil plants proved their affinity and connection to particular
trees and shrubs, as well as displaying considerable variation in shape, size and
ornamentation. Rahman et al. (2019) in their research of living pollen stressed the
‘overlapping and diverse morphological characters’ in the identification of pollen on
the species level.
It seems from the various examples given above and the comparison with living
forms in the present study that sculpture alone is not very useful for supra-generic
or even generic divisions. Therefore, sculptural elements are not used in the present
study as sole criteria for the identification of genera but are considered in combination
with some other distinguishing feature, such as the spore outline or nature of tetrad
mark. Potonie’s (1956) supra-generic classification, namely infra-turmae of spores,
based on sculptural elements is rejected in the present study for the reasons mentioned
above. Dettmann’s (1963) supra-generic classification with the exclusion of the infraturmae is adopted for Sporites.
Turmae are based on character of the aperture, whether monolete or trilete. Again,
there is a problem with that since one plant may produce spore/pollen with monolete,
dilete or trilete aperture, and often there is just a thinning of the exine apparent.
Therefore, the term ‘Turmae’ is abandoned in the present classification. Supra subturmae are based on the stratification of the exine, namely whether the exine has
resolved into an ektexine and an endexine by the formation of a cave or cavities
between the layers, or whether the exinal layers remain unseparated.
Equatorial features are used in the present classification for sub-turmae of the
cavate and acavate feature itself; for example, zonate, singulate or singulo-zonate.
The character of the zona is used as a criterion for generic diagnosis.
9
The diversity in size and sculpture of spores found within one and the same
sporangia was confirmed by the studies of Eggert and Taylor (1966): “The spores
exhibit a remarkable diversity in size and ornamentation ranging from smoothwalled immature forms to mature, highly ornamented types”. The variation within
one species in Eggert and Taylor’s study shows similarities to the fossil spores
of Raistrickia and Apiculatisporites on one hand, and to Punctatisporites and
Calamospora on the other hand.
Lindstrom et al. (1997) examined and studied pollen extracted from single
complete Glossopterid sporangia and found an enormous variation in the pollen
morphology.
The problem with the present intricate classification (e.g. Potonie) in use for
fossil dispersed spores and pollen was discussed and summed up by Balbach (1966)
as follows: “Although current systems of plant microfossil classification are usable
stratigraphically, the lack of a botanical taxonomic basis has led to the naming of a
multiplicity of species, many of doubtful biological validity. There should be no reason
why a botanically valid classification may not be made usable stratigraphically and
vice versa”.
Indeed, recent studies of spores and pollen isolated from fossil sporangia and
pollen sacs attached to fossil plants proved their affinity and connection to particular
trees and shrubs, as well as displaying considerable variation in shape, size and
ornamentation. Rahman et al. (2019) in their research of living pollen stressed the
‘overlapping and diverse morphological characters’ in the identification of pollen on
the species level.
It seems from the various examples given above and the comparison with living
forms in the present study that sculpture alone is not very useful for supra-generic
or even generic divisions. Therefore, sculptural elements are not used in the present
study as sole criteria for the identification of genera but are considered in combination
with some other distinguishing feature, such as the spore outline or nature of tetrad
mark. Potonie’s (1956) supra-generic classification, namely infra-turmae of spores,
based on sculptural elements is rejected in the present study for the reasons mentioned
above. Dettmann’s (1963) supra-generic classification with the exclusion of the infraturmae is adopted for Sporites.
Turmae are based on character of the aperture, whether monolete or trilete. Again,
there is a problem with that since one plant may produce spore/pollen with monolete,
dilete or trilete aperture, and often there is just a thinning of the exine apparent.
Therefore, the term ‘Turmae’ is abandoned in the present classification. Supra subturmae are based on the stratification of the exine, namely whether the exine has
resolved into an ektexine and an endexine by the formation of a cave or cavities
between the layers, or whether the exinal layers remain unseparated.
Equatorial features are used in the present classification for sub-turmae of the
cavate and acavate feature itself; for example, zonate, singulate or singulo-zonate.
The character of the zona is used as a criterion for generic diagnosis.