Department of Botany, Rhodes University, Grahamstown, South Africa.
Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, South Africa.
Ann Bot. 2020 Jun 1;125(7):1137-1149. doi: 10.1093/aob/mcaa048.
Complex modifications of angiosperm flowers often function for precise pollen placement on pollinators and to promote cross-pollination. We explore the functional significance of the unusually elaborate morphology of Gloriosa superba flowers, which are divided into one hermaphrodite meranthium and five male meranthia (functional pollination units of a single flower).
We used controlled pollination experiments, floral measurements, pollen load analyses and visitor observations in four populations of G. superba in South Africa to determine the breeding system, mechanism of pollination and role of flower in the promotion of cross-pollination.
We established that G. superba is self-compatible, but reliant on pollinators for seed production. Butterflies, in particular the pierid Eronia cleodora, were the primary pollinators (>90 % of visitors). Butterflies brush against the anthers and stigma during nectar feeding and pollen is carried on their ventral wing surfaces. Butterfly scales were positively correlated with the number of pollen grains on stigmas. We demonstrate that the styles were orientated towards clearings in the vegetation and we confirm that the highest proportion of initial visits was to hermaphrodite meranthia pointing towards clearings.
The flower morphology of G. superba results in effective pollen transfer on the wings of butterfly visitors. The style-bearing hermaphrodite meranthium of the flowers orientates towards open spaces in the vegetation, thus increasing the probability that butterflies land first on the hermaphrodite meranthium. This novel aspect of flower orientation is interpreted as a mechanism that promotes cross-pollination.
被子植物花朵的复杂修饰通常具有将花粉精确放置在传粉者上的功能，并促进异花授粉。我们探索了朱顶红花朵异常精细形态的功能意义，其花朵由一个雌雄同体的肉穗花序和五个雄性肉穗花序（一朵花的单个功能授粉单位）组成。
我们在南非的四个朱顶红种群中进行了控制授粉实验、花部测量、花粉负荷分析和访花者观察，以确定其繁殖系统、授粉机制以及花朵在促进异花授粉中的作用。
我们证实朱顶红是自交亲和的，但依赖于传粉者来产生种子。蝴蝶，特别是粉蝶科的 Eronia cleodora，是主要的传粉者（>90%的访客）。蝴蝶在取食花蜜时会刷到雄蕊和柱头，花粉则粘在它们的腹侧翅面上。蝴蝶鳞片与柱头上的花粉粒数呈正相关。我们证明了柱头的朝向与植被中的空地有关，并且证实了初始访问中指向空地的雌雄同体肉穗花序比例最高。
朱顶红花朵的形态导致了蝴蝶访客翅膀上有效的花粉转移。花朵的具柱头的雌雄同体肉穗花序朝向植被中的开阔空间，从而增加了蝴蝶首先降落在雌雄同体肉穗花序上的可能性。这种花朵定向的新颖方面被解释为促进异花授粉的机制。
