101-4 A Seed Plant Reproductive Morphospace

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns

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Seed plants have evolved extremely diverse reproductive structures, although some clades clearly exhibit greater disparity than others. Quantifying differences in the evolution of reproductive disparity across seed plants is challenging because reproductive structures are not easy to compare; they are often highly divergent and homologies among organs are uncertain. Here we develop a discrete character scoring system to address some of these challenges, in which we apply a set of 52 morphological characters iteratively to each organ that composes a given reproductive structure. We then assign organs to a set of categories based on their functionality and the branching architecture of the reproductive structure, enabling us to calculate morphological distances between analogous organ types for any reproductive structure. We also perform a separate analysis where we collapse character state scorings across all organs into a single combined set that reflects the sum of shape features present in a reproductive structure regardless of organ number or homology. We use these two approaches to ask how extant seed plant clades occupy a common reproductive morphospace. In general, major extant gymnosperm clades (i.e., families or orders) occupy relatively small regions of morphospace and show more partitioning by clade, whereas high-level angiosperm groups (e.g., magnoliids, eudicots) occupy broader and overlapping regions of character space. Pairwise morphological distances among angiosperm taxa also increase more rapidly with pairwise divergence ages than those of gymnosperms. Extant gymnosperms therefore appear to show lower rates of reproductive evolution than angiosperms, as their reproductive structures occupy more restricted areas of morphospace and fill space more slowly through time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7913

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