Comparative floral ecology and breeding systems between sympatric populations of &lt;i&gt;Nothoscordum bivalve&lt;/i&gt; and &lt;i&gt;Allium stellatum&lt;/i&gt; (Amaryllidaceae)

Daniel S Weiherer,Kayla Eckardt,Peter Bernhardt

doi:10.26786/1920-7603(2020)585

Abstract

We compared the floral biology of two sympatric populations of closely related species over two seasons. In 2018, Nothoscordum bivalve (L.) Britton bloomed from April 23 to May 7 and Allium stellatum Nutt. Ex Ker Gawl bloomed from August 28 to October 4. Erect, white flowers of N. bivalve were scented and had septal nectaries. Erect, pink-purple flowers of A. stellatum had septal nectaries, no discernible scent, and a style that lengthened over the floral lifespan. Both species were pollinated by bees with the most common geometric mean of body dimensions between 2-3 mm. Most bees carried pure loads of the host plant’s pollen. Despite phenological isolation, the two herbs shared three bee species. Allium stellatum was also pollinated by the beetle Chauliognathus pensylvanicus DeGeer (Cantharidae). Tepal nyctinasty ensured mechanical self-pollination in N. bivalve. Protandry occurred in A. stellatum. In N. bivalve, the proportion of pollen tubes penetrating ovules was highest in bagged, self-pollinating flowers. However, in A. stellatum it was highest in exposed flowers and hand cross-pollinated flowers. Fruit set in N. bivalve was highest in exposed and bagged, self-pollinating flowers. In A. stellatum, fruit set was highest in both exposed and hand cross-pollinated flowers. Seed set was the same among all treatments for both species. We interpret these results as evidence that A. stellatum is a self-incompatible, obligate outcrosser. Nothoscodum bivalve is a self-compatible, obligate inbreeder employing mechanical and insect-mediated self-pollination. Outbreeding depression appears to occur in N. bivalve with a partial trend towards intraspecific cross-incompatibility.

Highlights

Understanding how plant reproduction is altered by human activity is essential for the conservation of species and the practice of agriculture
The flowering of N. bivalve was relatively short-lived but flowering stems were at a higher density compared to A. stellatum
The flowering period of N. bivalve occurred in April and May as predicted by Baskin & Baskin (1979)

Summary

Introduction

Understanding how plant reproduction is altered by human activity is essential for the conservation of species and the practice of agriculture. The Order Asparagales contains commercially important species with ornamental, medicinal, and agricultural cultigens (Pires et al 2006; Christenhusz & Byng 2016). This is important in the genus Allium ss and its allies in the Amaryllidaceae (Angiosperm Phylogeny Group 2009), previously Alliaceae (The Angiosperm Phylogeny Group 2003) and/or Liliaceae (Cronquist & Takhtadzhi︠a︡n 1981). Information on the pollination and breeding systems of native populations of Allium species and their allies in North America lags behind nearly two centuries of research on cultigens. It is distributed from Texas to Canada in states along the Mississippi river and can be found

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