Heterostyly and pollen dimorphism of <i>Menyanthes trifoliata</i>

Abstract

<i>Menyanthes trifoliata</i> L., a heterostyly plant, is an endangered species in Korea. Floral morphology has been published for <i>M. trifoliata</i>, but few works have concentrated on pollen dimorphism differences accompanied by floral dimorphism. Here, we conducted a comparative morphological study of two morphs to investigate a dimorphism system with Korean populations. Pollen morphological characteristics were observed with a light microscope and a scanning electron microscope. For the pin type, pollen size is 36.01 ± 2.01 µm, whereas for the thrum type it is 41.28 ± 2.58 µm in terms of the equatorial diameter. The two morphs have a small apocolpium field at 5.62 ± 0.30 for the pin type and 6.24 ± 0.70 for the thrum type. The configuration of the aperture was tricolpate with a striate ridge in the two morphs. However, they have different pollen shapes and sizes, stigma shapes, and apocolpium sizes. <i>M. trifoliata</i> only has different pollen sizes and shapes between European populations and Korean populations. Nevertheless, Korean populations also show pollen dimorphism correlated with their floral dimorphism.