Abstract Detail

Anatomy and Morphology

Tsai, Tim [1], Diggle, Pam [1], Frye, Henry [1], Jones, Cynthia [1].

Spectacular receptacular nectar tubes of Pelargonium (Geraniaceae): Development, length variation, and histology.

Pollinator mediated selection is recognized as a critical driver of the morphological evolution of flowers. Floral nectar tubes are often interpreted as key morphological traits associated with diversification because they enhance specialized relationships of flowers with distinct pollinators. The predominantly South African plant genus Pelargonium is one of the large Cape radiations in which pollinator shifts have been hypothesized to drive diversification. Within Pelargonium, nectar tube lengths range from less than 0.5 mm to over 100 mm. While developmental mechanisms generating such diversity are of inherent interest, a further motivation for investigating nectar tube development in Pelargonium was to explore homology of the tube itself, which has been variously described as a “sepal spur adnate to the pedicle,” “hypanthial,” or “receptacular.” We used SEM, growth analysis, histology and epidermal peels to characterize nectar tube development in two closely-related species of Pelargonium that differ three-fold in nectar tube length. We found that nectar tubes are initiated at the same developmental stage in both species, when buds are less than 1 mm in length. At this stage, all floral whorls have been initiated. The dorsal antisepalous stamen is displaced centripetally, creating an enlarged space between the two dorsal antipetalous stamens. The nectar tube originates as a slight concavity in this enlarged space on the receptacle, centripetal to the dorsal sepal. Subsequent formation of the tube occurs though intercalary elongation of the receptacle at similar rates in both species until just before anthesis, when the longer-tubed species experiences a burst of elongation that persists for up to four days following anthesis. At maturity, epidermal cells on the dorsal surface of the nectar tube are twice as along in the long-tubed species. Histological sections emphasizing vascular patterns show divergence of petiole bundles directly from the petiole acropetally to the dorsal surface of the nectar tube. We see no vascular evidence that supports a hypothesis of a sepal spur adnate to the pedicle.

1 - University Of Connecticut, Ecology and Evolutionary Biology, U 3043, 75 N. Eagleville Rd., Storrs-Mansfield, CT, 06269, USA

Keywords:
none specified

Presentation Type: Oral Paper
Session: 20, Anatomy and Morphology
Location: Fort Worth Ballroom 7/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 11:15 AM
Number: 20013
Abstract ID:252
Candidate for Awards:None