Unlocking the secrets of parasitic plants: A comparative study of the development and floral morphoanatomy of Pholisma (Lennoaceae)

Abstract

Pholisma belongs to the family Lennoaceae, classified as obligate root holoparasites. Most existing studies are limited to addressing only P. arenarium. In this study, morphoanatomical and developmental aspects of flowers of the three species comprising Pholisma are described using histological embedding techniques in Paraplast and LR- White and observations by light microscopy and scanning electron microscopy. Similarities found in the three species include the presence of trichomes on the sepals, each carpel folding independently. Each carpel has transmitting tissue, and an empty cavity is distinguished in the centre of the style. The stigma is crateriform and of the wet type. Sporogenesis, gametogenesis, and floral development follow a similar pattern in the three species. Differences among species include the position of the stamens, pollen morphology, type of inflorescence, and colour of flowers and inflorescences. In P. arenarium, the stamens are located below the stigma height, and the pollen is tetracolporate and psilate; in P. sonorae, the stamens are at the same height as the stigma, and the pollen is tricolporate and reticulate; and in P. culiacana, the stamens are above the stigma height, and the pollen is tricolporate and psilate. The inflorescences in both P. arenarium and P. sonorae are cymes; the corolla colour is white with purple lines extending from the limb to the corolla tube. In contrast, the inflorescence in P. culiacana is a capitulum type, and the corolla colour is white with pink margins. The characters found in the three species of Pholisma are compared with some genera comprising the family Ehretiaceae.