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Abstract Detail

Development and Structure

Smith, Annika [4], Stanley, Edward L. [1], Struwe, Lena [2], Garcia, Nicolas [3], Soltis, Douglas E. [4], Soltis, Pamela S. [4].

Floral vascular architecture: Nectar spurs in the nasturtiums (Tropaeolum).

How much does the underlying floral vasculature vary beneath seemingly constant morphological characters? And does floral vasculature have anything to tell us about developmental constraints? Historically dismissed as unpredictable in systematic studies, floral vasculature may be viewed in the context of a possible developmental constraint with a potential role in generating morphological novelty. We investigate the relationship between floral morphology and anatomy in the genus Tropaeolum, which has a nectar spur that forms late in development on the receptacle of the flowers. We found that while the nectar spur is a synapomorphy of Tropaeolum, present in each of the approximately 100 species, the underlying vasculature of the flower is highly variable across species, but also apparently constrained to a strict bilateral symmetry. Floral nectar spurs have formed repeatedly in both monocots and eudicots, but Tropaeolum is the only clade with well-developed nectar spurs that form on the floral receptacle. The floral receptacle is a point of connection for the other floral organs, but its role in producing floral variability (via expansion or elaboration) is often overlooked in comparison to other floral organs such as petals. We present models of the underlying floral vascular architecture of the receptacular spur in a range of Tropaeolum species, focusing on transition of vascular traces from the pedicel, through the receptacle and spur, and into the rest of the flower. We built three-dimensional models of floral vascular architecture by segmenting nano-CT scans of three closely related Chilean species with variable lengths in nectar spurs: Tropaeolum azureum, T. brachyceras, T. tricolor, and the naturally occurring hybrid T. x tenuirostre. In addition, we also compared these with more distantly related species (T. ciliatum and T. majus), as well as mutant flowers of T. x tenuirostre and T. majus and spur-less cultivars of T. majus. We found significant variability in the vascular architecture at both superficial levels of the flower (e.g. venation of the petals) and at deeper levels of the construction of the flower (in the receptacle). These results point to striking variability in the vascular architecture of a synapomorphic character and raise further questions about the role of vascular architecture as a developmental constraint.

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1 - University Of Florida, Florida Museum Of Natural History, Department of Herpetology, 1659 Museum Rd., Gainesville, FL, 32611, USA
2 - Rutgers University, Ecology, Evolution, & Natural Resources, 237 Foran Hall, 59 Dudley Road, New Brunswick, NJ, 08901, United States
3 - Universidad De Chile, Herbario EIF, Av. Santa Rosa 11315, La Pintana, Santiago, SM, 8820808, Chile
4 - University Of Florida, Florida Museum Of Natural History, PO Box 117800, Gainesville, FL, 32611, United States
5 - University Of Florida, Florida Museum Of Natural History, PO Box 117800, Gainesville, FL, 32611, United States

nectar spur
comparative anatomy
floral morphology
floral evolution
developmental constraint

Presentation Type: Oral Paper
Session: DS1, Development and Structure I
Location: /
Date: Tuesday, July 20th, 2021
Time: 1:45 PM(EDT)
Number: DS1015
Abstract ID:895
Candidate for Awards:Katherine Esau Award

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