Flammable resin in Vellozia variabilis (Velloziaceae): Gland structure and chemical composition

Species of Vellozia are prominent on rocky outcrops, they are known for their unique flammability. The presence of resin in their leaves is widely recognized, although the secretory systems related to this resin have not been described until now. In this paper, we investigate the structure of the resin glands in leaves of Vellozia variabilis using light and transmission electron microscopy. To investigate the chemical composition of the resin we performed phytochemical tests. The resin glands covered the entire margin of the leaf blade and the adaxial surface of the leaf sheath distal region. The secretory cells exhibited ultrastructural features of intense metabolic activity and prominent smooth endoplasmic reticulum. The numerous vesicles observed in the secretory cells seem to be related to the secretion of the resin. Osmiophilic droplets were observed in the protoplast and in the secretory cell walls, indicating a possible lipophilic content. The resin produced by the leaves of V. variabilis may be categorized as a mixed resin as it exhibits the presence of both flavonoid and terpenoid constituents. This resin covers the entire leaf surface and accumulates at the leaf base. Putative functions of the resin include ultraviolet screening, protection against water loss and high temperatures, and deterring herbivores. Besides all of these possible functions, the resin of V. variabilis plays an important role in an interesting survival strategy. It protects the plant meristem from fire damage by facilitating the rapid burn of the plant and, thus, protecting the plant fire-sensitive tissues.