ULTRASTRUCTURAL STUDIES OF IN SITU DEVONIAN SPORES: BARINOPHYTON CITRULLIFORME

Area of Science:

• Paleobotany
• Evolutionary Biology
• Reproductive Biology

Background:

• The evolution of heterospory, the production of spores of different sizes, is a critical event in plant evolution.
• Devonian period flora provides crucial insights into early land plant adaptations.

Purpose of the Study:

• To investigate the spore morphology and organization within the sporangia of Barinophyton citrulliforme.
• To determine the functional significance of different spore types found within the same sporangium.
• To elucidate the evolutionary stage of heterospory represented by Barinophyton citrulliforme.

Main Methods:

• Microscopic examination of sporangia from Barinophyton citrulliforme.
• Ultrastructural analysis of microspore and megaspore walls.
• Comparative analysis of spore size and morphology.

Main Results:

• Sporangia of Barinophyton citrulliforme contain both microspores (up to 50 μm) and megaspores (up to 900 μm).
• Microspores have a homogeneous sporoderm with a separable outer layer.
• Megaspore walls exhibit a spongy organization due to loosely arranged sporopollenin units.
• Ultrastructural evidence indicates both spore types were functional, not abortive.

Conclusions:

• Barinophyton citrulliforme demonstrates a significant phase in the evolution of heterospory.
• This taxon suggests that sex determination in spores may have occurred within the same sporangium before the evolution of distinct micro- and megasporangia.
• The findings contribute to understanding the early evolution of reproductive strategies in land plants.