Flower and fruit micromorphology and anatomy in Circaea lutetiana (Onagraceae)
Keywords:
epidermal trichomes, gynoecium, pyrenarium, seed coat, vascular anatomyAbstract
Questions: In the genus Circaea, many important floral and fruit traits remain insufficiently studied which precludes congruence between molecular and non-molecular data in systematics and hampers understanding of morphological evolution within the Onagraceae family. Location: fixed specimens of Circaea lutetiana flowers and fruits from Lviv and Zakarpattia regions. Materials and methods: permanent and temporal preparations, light microscope technique, gynoecium micromorphology, vascular anatomy, fruit and seed coat anatomy. Nomenclature: Wagner et al. 2007, POWO 2026. Results: The investigation revealed that sepals, petals, stamens, nectary disc, and the style are all inserted at the top end of the ovary neck, previously termed the floral tube or hypanthium. The bilocular ovary is composed of synascidiate and symplicate zones with apical septa in the latter. Each ovule is attached to the top of synascidiate zone and is provided by trans-septal vascular bundles from both septal veins. Two dorsal and two septal veins supply the inferior ovary till the top of the ovary neck, where they branch into traces of floral organs and vascular bundles supplying the nectary. After anthesis, ovary neck separates from the locular part and falls away together with the attached floral organs. Fruit wall is largely parenchymatous. It is composed of unilayered exocarp, homogenous compact mesocarp and unlignified endocarp. During fruit development, the inner 1–2 subepidermal layers of the mesocarp becomes to lignify. Two types of one-celled epidermal trichomes were found on the ovary wall: lignified stiff uncinate (hooked) and glandular clavate-tipped hairs. Seed coat is composed of a multilayered testa and bilayered tegmen. The mesotesta consists of 5–6 layers; endotesta and exotegmen are lignified. The fruit type is defined as a two-stoned pyrenarium based on the ovary structure and fruit wall anatomy. Conclusions: Our study provides deeper insight into the internal structure of flower and fruit of Circaea lutetiana. The inner gynoecium structure, fruit wall and seed coat anatomy were examined for the first time in the genus Circaea. Newly revealed traits, such as lignified subepidermal layer of the mesocarp, trans-septal ovule supply, and glandular trichomes, also occur in Epilobium and Oenothera species, offering new perspectives on the morphological evolution within the Onagraceae.
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