Floral anatomy, micromorphology and visitor insects in three species of Aristolochia L. (Aristolochiaceae)

Abstract

The genus Aristolochia L. has a specialised pollination system based on flowers that represent traps for insects. The floral anatomy and micromorphology of the perianth were studied to detect structural characters and secretory cells that are essential for the pollination and reproduction in A. esperanzae, A. fimbriata and A. triangularis. Additionally, we identified the insects collected inside the flowers in natural populations of the north of Argentina. Our observations indicate the presence of osmophores in the limbs of A. esperanzae and A. triangularis, and in the tube of A. fimbriata, because in this last species the fimbriae probably play the first optical attraction role. The papillose cells and epicuticular waxes in the limbs and tube entrances, particularly in A. esperanzae and A. fimbriata, ensure that insects slip into the tube, and the nonsecretory conical hairs of the tube, when turgid, guide the insects to the utricle. Idioblasts on the abaxial surfaces of the tubes andutricles were observed in A. esperanzae and A. fimbrita, and probably represent ethereal oil cells that protect flowers from predation. Secretion of sugar was confirmed on all internal surfaces of the utricle in the three species, and was more abundant at the entrance. The insects were diverse species of Diptera (Sarcophagidae, Muscidae, Ulidiidae, Drosophilidae and Anthomyiidae) and Coleoptera (Staphylinidae), although pollen loads on the body were only detected on specimens of Ulidiidae and Sarcophagidae.