Sprecher
Beschreibung
Pararaucaria patagonica seed cones are remarkably well-suited for in-depth study of their phyllotaxis and architecture thanks to the highly detailed preservation of their gross morphology and anatomy. Originating from the Middle Jurassic of Argentina, these cones can be either long and cylindrical or short and ovoid at maturity. Although superficially distinct, numerous anatomical studies have confirmed that both forms belong to Pararaucaria patagonica. However, it is currently unknown how these cones’ phyllotaxis and construction result in this varied morphology. Here we present two strategies for the construction of slender conifer cones: stretching or stacking the cones’ seed spirals. Micro-CT and digital segmentation were used to reconstruct the internal seed arrangement of Pararaucaria patagonica in three-dimensions, revealing 2,3 phyllotaxis. Statistical analysis shows that cone width does not increase with length, but their parastichies rotate more times around the axis as the cone lengthens. Because Pararaucaria is extinct and has no living relatives, Picea orientalis was selected as a modern analog representing a long, thin cone. Although morphologically similar, these cones have 3,5 phyllotaxis with widths that scale with cone length. Additionally, its parastichies stretch to fit increased cone length, instead of adding more rotations. In contrast to Pararaucaria and Picea orientalis, araucariaceous cones, exemplified by Araucaria mirabilis, widen their girth and parastichies instead of lengthening. Furthermore, we demonstrate that the ontogeny of a fossil seed cone can be predicted by its phyllotaxis and parastichy chirality. These results shed light on the relationship of phyllotaxis and conifer seed cone construction.