The upcoming discussion will update you about the differences between Angiosperm and Gymnosperm.
1. Vascular Tissue:
Angiosperms have vessels in secondary xylem. However, some Magnoliid angiosperms lick vessels (e.g. the Winteraceae, Tetracentraceae, Trochodendraceae, etc.). Most gymnosperms lack vessels, except the Gnetales. Hence, the presence of vessels cannot be used as evidence that a plant is an angiosperm.
2. Leaves:
Angiosperms have either parallel or reticulate venation with intercostal veins. On the other hand gymnosperms often have parallel venation with few branching (intercostal) veins. Extant gymnosperms such as Gnetum have strikingly angiospermous leaves. Hence, leaf morphology can only provide supportive, not conclusive evidence of a plant being an angiosperm.
3. Flowers:
Angiosperms are flowering plants. However, the presence of a flower, as a character to distinguish angiosperms from gymnosperms, is a matter of artificial definition, as it is not possible to define a flower with morphological precision, so as to exclude the cone or cluster of fertile sporophylls that characterize the gymnosperms.
4. Pollen Wall Structure:
Outer wall of the pollen grain is the ektexine. In angiosperms, ektexine (outer wall of the pollen grain) is either columellate or tectate (Fig. 10.1). Gymnospermous pollen are atectate i.e., lacks tectae. On the other hand endexine (the inner wall of the pollen) is spongy in gymnosperms, but not spongy in angiosperms.
5. Pollen Apertures:
Advanced angiosperm pollen are triaperturate i.e., have three apertures whereas gymnosperms and Magnoliid angiosperms (most primitive group) pollen are uniaperturate i.e., have only one aperture. In the more advanced angiosperms, the pollen may also be monocolpate and tricolpate. So, pollen aperture number cannot be used to infer whether a plant is a gymnosperm or an angiosperm.
6. Reduced Female Gametophytes:
Angiosperms have no archegonium as is found in gymnosperms. However, some gymnosperms also lack archegonia, e.g. within Gnetales, only Ephedra has one.
7. Carpels:
The best evidence that a plant is an angiosperm is the presence of ovules enclosed within a carpel (mega sporangium within an in-rolled megasporophyll). However, according to Endress, none of these carpels are truly closed because secretions from the inner lining of the carpel fill the gap.
8. Double Fertilization:
In angiosperms, triploid endosperm is produced by the fusion of a sperm nucleus and a polar nucleus. A similar form of double fertilization has been found to occur in Ephedra (Gnetales), but no endosperm is formed, instead simply multiple embryos are formed.
Friedman hypothesized that if this process was homologous with angiosperms, endosperm could have evolved from such “supernumerary fertilization events.”
