Rhizome Thickness Influences the Oil Yield and Oil Constituents in <i>Homalomena aromatica</i> (Spreng.) Schott

ABSTRACT Homalomena aromatica is an economically important essential oil‐producing plant. The rhizome is a commercial source of essential oil useful for high‐grade perfumery and therapeutic applications. It is mainly collected from wild sources. The present study aims to investigate the histochemical localization of oil‐secreting idioblasts and the variability in oil composition in commercial samples. The histochemical study revealed that essential oil is synthesised in oil cells and oil cavities distributed in the rhizome tissues. The larger oil cavities (521 ± 59.4 μm in size) synthesise essential oil and resin, whereas the smaller oil cells (67.2 ± 7.4 μm in size) synthesise only essential oil. The spatial distribution demonstrates that the oil cavities were densely present in the inner ground tissue region, whereas the oil cells were abundant in the cortex ( p &lt; 0.05 ). The different grades of commercial rhizome samples, that is, thickness up to 10 mm (narrow rhizomes, NR), 10 to 20 mm (medium‐sized rhizomes, MR), and 20 to 30 mm (thick rhizomes, TR) showed variation in essential oil yield and composition, fibre content, and distribution of fibre cells. The study demonstrated that the oil yield is negatively correlated with rhizome thickness, fibre content, and density of fibre cells in tissue. The oil of H. aromatica is dominated by linalool (44.18%–61.4%) followed by terpinene‐4‐ol (6.45%–13.16%) in the rhizomes of different thicknesses. These major constituents also negatively correlate with rhizome thickness and significantly decrease in the TR samples. The study concludes that the NR grade rhizomes are better for higher oil yield and linalool and terpinene‐4‐ol content than the TR grade of H. aromatica rhizomes.