Tri-Phyletic Origin of Gymnosperms

Tri-Phyletic Origin of Gymnosperms:-

> Greguss (1972), in the latest edition of his book entitled “Identification of Living Gymnosperms on the Basis of Xylotomy”, pleaded for a tri-phyletic origin of gymnosperms. He opined that on the basis of Xylotomy (wood-anatomy) three well-defined evolutionary series may be traced among the existing

gymnospermous taxa.

> All these three series among existing gymnosperms have definite correlations with three types of

pteridophytes, another tri-phyletic group:

i. Cycadales (Cycas), Ginkgoales (Ginkgo), Araucariaceae, Podocarpaceae and probably Taxales showing correlations with Pteropsida of Pteridophytes.

ii. Cupressaceae showing correlations with Sphenopsida of Pteridophytes.

iii. Pinaceae and Taxodiaceae showing correlations with Lycopsida of Pteridophytes.