Revealing the hidden laticifers of Urticaceae: morphology, ontogeny, and latex composition

Laticifers are secretory structures recognized for the economic and biological importance of latex. They may be composed of a single cell or a series of interconnected cells and occur in approximately 10% of angiosperms, including members of Urticaceae. This family represents a valuable model for laticifer studies because its secretory system is inconspicuous: the latex is colorless and of low viscosity, lacking the typical milky appearance, and the laticifers are difficult to detect. Here, we expand knowledge of laticifers in Urticaceae by examining their distribution, morphology, developmental origin, and in situ chemical composition. Leaves, stems, buds, and inflorescences were sampled from eight species representing eight genera and four tribes. Laticifers were found to be more widely distributed than reported, occurring not only in bark and sepals but also in leaf, stems, inflorescence axes, filaments, ovaries, and pedicels. All species possess articulated laticifers derived from two to five precursor cells that undergo dissolution of terminal walls during differentiation. The latex contains phenolics, proteins, alkaloids, lipids, polysaccharides, and rubber particles, with interspecific variation. These findings refine the understanding of laticifer structure and distribution in Urticaceae, clarify misconceptions, and document their occurrence for the first time in Boehmeria Jacq., Myriocarpa Benth., Phenax Wedd., and Pilea Lindl.