Anatomical studies of two Chilean Podocarpaceae species: insights to the seed cone and leaf morphological evolution of the family

ANDRUCHOW, A.; AAGESEN, L.; POZNER, R.

Tucson

Congreso; Botany 2019; 2019

Botanical Society of America

The Podocarpaceae include ca. 200 extant species within 18 genera, being the conifer family with the second-highest diversity in the world. Most modern phylogenetic analyses of the family are based on only-extant taxon samplings. This approach is clearly suboptimal when considering that the evolutionary history of the Podocarpaceae goes back at least to the Jurassic and shows a combination of numerous divergence and extinction events in deep time followed by relatively recent radiations. In order to understand the early morphological evolution of the family, it is crucial to develop integrative studies combining molecular data and detailed morphological and anatomical information for both extinct and extant species. In this context, we have developed a research program including (i) the description and reconstruction of Mesozoic and Cenozoic fossil species, (ii) the description of particular extant species that are morphologically and/or anatomically poorly understood, and, (iii) the development of a total evidence phylogenetic analysis. The family Podocarpaceae encompasses a wide morphological diversity of photosynthetic structures and megasporangiate cones, which are still poorly understood for several of its extant genera. Consequently, the evolution patterns that led to this high morphological diversity seen today have not been deeply explored. In this context, the need for an integrative approach to study Podocarpaceae?s evolutionary history becomes evident. In this contribution, we present the anatomical description of the leaves and seed cones of two Podocarpaceae species from Southern Chile, Saxegothaea conspicua Lindl. and Lepidothamnus fonkii Phil. and integrate this new evidence with information available in the literature on other extant and fossil podocarp species. We interpret the high morphological diversity of the family in a phylogenetic context, with the overall objective of shedding light onto certain aspects of the ancestral configuration of the leaves and seed cones within the Podocarpaceae. Modern phylogenetic analyses of the family retrieve two sister clades, namely tropical and prumnopityoid. Saxegothaea is usually recovered at the base of the tropical clade, which is the most diverse (ca. 88% of the podocarp species), whereas Lepidothamnus is recovered in varying positions within the prumnopityoid clade. These two genera are markedly different in leaf, seed cone, and pollen morphology. We propose that they both show a mosaic of characters, being the scale-like leaves of Lepidothamnus most similar to what we interpret to be the ancestral podocarp leaf morphology, and the multiseeded cones of Saxegothaea most similar to our interpretation of the ancestral seed cones of the family.