Comparative leaf blade and petiole anatomy of selected Thai species of Helicteres (Malvaceae)

WIROT KESONBUA (Department of Biological Sciences and Health, Faculty of Science, Ubon Ratchathani University. 85 Sathonlamak Rd, Mueang Si Khai, Warin Chamrap, Ubon Ratchathani 34190, Thailand)
SEKSUN POOMPO (Program of Biology, Department of Biological Sciences and Health, Faculty of Science, Ubon Ratchathani University. 85 Sathonlamak Rd, Mueang Si Khai, Warin Chamrap, Ubon Ratchathani 34190, Thailand)
ANITTHAN SRINUAL (Department of Biology, Faculty of Science, Srinakharinwirot University. 114 Sukhumvit 23, Khlong Toei Nuea, Watthana, Bangkok 10110, Thailand)

Biodiversitas Journal of Biological Diversity
Vol. 27 No. 9 (2026)

Abstract. Kesonbua W, Poompo S, Srinual A. 2026. Comparative leaf blade and petiole anatomy of selected Thai species of Helicteres (Malvaceae). Biodiversitas 27 (9): d270921. https://doi.org/10.13057/biodiv/d270921. Overlapping morphological characters can complicate the identification of Helicteres species (Malvaceae), particularly when reproductive structures are unavailable. This study evaluated the taxonomic utility of leaf-blade and petiole anatomy in nine of the 12 currently recognized Helicteres species in Thailand. Each species was represented by one natural population, with five individuals sampled per population and five fully expanded leaves examined per individual. Epidermal peels and transverse sections of the leaf blade and petiole were examined using light microscopy. All species possessed anomocytic stomata, dorsiventral mesophyll, collateral vascular bundles, druse crystals, mucilage-containing structures, and glandular trichomes, whereas several characters varied among taxa. Helicteres isora, Helicteres obtusa, Helicteres prostrata, and Helicteres thailandica were amphistomatic, while the remaining species were hypostomatic. Striate cuticles occurred only in H. isora and H. prostrata, and prismatic crystals were recorded in H. elongata and H. thailandica. Additional interspecific variation occurred in epidermal cell shape, stellate and simple trichomes, midrib outline, vascular-bundle number and shape, and petiole vascular-bundle/fiber-sheath organization. These character combinations were used to construct a provisional anatomical identification key for the nine examined species. Internal application of the key correctly assigned all 45 examined individuals; however, because the same specimens were used to establish the character states and construct the key, this does not constitute independent validation. The results demonstrate the potential of comparative leaf and petiole anatomy to complement morphological identification of Thai Helicteres, while broader applicability requires testing with independent specimens and replicated populations.