Floral development elucidates the formation of a tubular calyx and connate stamens in Cecropieae species (Urticaceae)

Premise: Celtis is the most species-rich genus of Cannabaceae, an economically important family. Celtis species have been described as wind-pollinated and andromonoecious. However, the andromonoecy of Celtis has been debated because there are reports of monoclinous flowers with non-opening anthers on short filaments. Our objective was to study the floral morphogenesis of Celtis to establish the breeding system and to better understand the developmental patterns that lead to the formation of reduced flowers in the genus. Methods: Flowers and floral buds of Celtis species were studied using scanning electron microscopy, high-resolution x-ray computed tomography, and light microscopy. Results: All flowers initiate stamens and carpels during early floral development, but either stamens or carpels abort during later stages. Thus, at anthesis, flowers are either functionally pistillate or functionally staminate. In pistillate flowers, stamens abort late and become staminodes with normal-looking anthers. These anthers have no functional endothecium and, in most of the species studied, produce no viable pollen grains. The gynoecium is pseudomonomerous, and its vascularization is similar in the sampled species. In staminate flowers, the gynoecium aborts early resulting in small pistillodes. No vestiges of petals were found. Conclusions: The species studied are monoecious and not andromonoecious as described earlier. The absence of petals, the carpel and stamen abortion, and the pseudomonomerous gynoecium result in the reduced flowers of Celtis species. The use of high-resolution x-ray computed tomography was essential for a more accurate interpretation of ovary vascularization, confirming the pseudomonomerous structure of the gynoecium.

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Floral morphogenesis of Celtis species: implications for breeding system and reduced floral structure

Leme

Staedler

Schönenberger

et al. 2021

American J of Botany

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A comparative approach reveals diversity of floral developmental processes in Urticaceae

Pedersoli

Staedler

Schönenberger

et al. 2022

Botanical Journal of the Linnean Society

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Most species of Urticaceae, the nettle family, have small and inconspicuous, diclinous flowers, in which the perianth, androecium and gynoecium tend to vary in number. Our objective was to study the morphology of the developing flowers of seven species of Urticaceae to understand the pathways that lead to the different patterns of floral reduction and the complex development of pseudomonomerous gynoecia. Buds and flowers were prepared for electron and light microscopy. Vascularization was studied via high resolution X-ray computed tomography micro-CT. Only one whorl of perianth organs is initiated, except for Phenax sonneratii, the flower of which is achlamydeous; variation in perianth merosity results from absence of organs from inception; dicliny results from the absence of stamens from inception (pistillate flowers) and from pistil abortion at intermediate developmental stages (staminate flowers). The gynoecium results from a primordium that divides partially forming two congenitally united primordia (most species) or from a single primordium that apparently does not divide. The gynoecium is served by a single (four species), or two vascular bundles. This second condition is expected for a pseudomonomerous gynoecium. Pistillode or rudimentary carpels occur in staminate flowers. The comparison among species shows that the developmental processes acting in the floral construction in Urticaceae is diverse.

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Flower morphogenesis and gametophyte fertility attest to the rare condition of gynomonoecy in Parietaria debilis (Urticaceae)

Pedersoli

Teixeira

2020

Botany

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Parietaria debilis is gynomonoecious, a rare condition in the Urticaceae family and among angiosperms. Apetalous flowers of two different morph types (monoclinous, pistillate) occur in the same inflorescence and are reduced in size and in the number of whorls and of organs per whorl. The objective of the present study was to compare the morphogenesis of monoclinous and pistillate flowers in order to understand if the monoclinous flowers produce fertile gametophytes and to determine the pathways leading to the absence of stamens and to the changes in number of whorls and organs per whorl. Flower buds and flowers (non-fertilized, fertilized) were processed for surface and anatomical studies. Pollen ultrastructure and viability was determined. Inflorescences with fertilized flowers were checked for the presence and location of fruits/viable seeds. The monoclinous flower has four sepals, four stamens and a uniovulate pseudomonomerous gynoecium. In the pistillate flower the stamens are absent or, rarely aborted. No petals are formed. The gynoecium is pseudomonomerous, originated as a central primordium that differentiates into two carpels, but only one develops and houses an ovule. Monoclinous and pistillate flowers produce viable seeds. Thus, our data confirmed that this species is indeed gynomonoecious.

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Floral development elucidates the formation of a tubular calyx and connate stamens in Cecropieae species (Urticaceae)

Cited by 3 publications

References 61 publications

Floral morphogenesis of Celtis species: implications for breeding system and reduced floral structure

Floral morphogenesis of Celtis species: implications for breeding system and reduced floral structure

A comparative approach reveals diversity of floral developmental processes in Urticaceae

Flower morphogenesis and gametophyte fertility attest to the rare condition of gynomonoecy in Parietaria debilis (Urticaceae)

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