, Volume 42, Issue 4, pp 247-260
Date: 03 Aug 2011

Morphogenetic lability of the Ruppia maritima (Ruppiaceae, Alismatales) reproductive organs: From two lateral flowers to a terminal flower

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Flowers of Ruppia are usually arranged into an open two-flowered spike, but sometimes two lateral flowers are congenitally united with each other forming a terminal flower-like structure. This deviation from the morphogenesis of reproductive structures typical of Ruppia resembles those described in well-studied mutants of the model organisms of developmental genetics, such as Arabidopsis and Antirrhinum. A study of Ruppia allows the morphogenetic lability of this trait to be traced in natural populations. These data are important for understanding the evolutionary transition from open to closed inflorescences. This paper describes the first data on the frequencies of terminal flower-like structures in natural populations of Ruppia maritima as well as on the specific features of their morphogenesis. The vascular supply in the inflorescences with free and fused flowers is also compared for the first time. It has been demonstrated that the frequency of inflorescences with fused flowers considerably varies between different populations. The data on variation in the number of organs in flowers of plants from different populations suggest that an increased size of floral primordia is a factor enhancing their fusion into a joint primordium of the terminal structure. The vascular system of the R. maritima inflorescences with united flowers is similar to the vascular system of a single flower; moreover, nothing contradicts the hypothesis on a terminal position of this structure. The R. maritima inflorescences with united flowers frequently contain transversal stamens with an inverted polarity. Presumably, this is the first case of recorded inversion of relative polarity of stamens and carpels in angiosperms.