A comparative study of the petiole anatomy in the tribes Forsythieae (Abeliophyllum, Forsythia) and Fontanesieae (Fontanesia), including one related genus Myxopyrum belonging to Myxopyreae, was carried out using light microscopy. The anatomical characteristics of the distal, medial and proximal parts of the petiole were studied to document any differences. We are described in detail based on their quantitative and qualitative characteristics. Three crystal types (acicular, druse, and prismatic crystals) were found in both Fontanesia and Myxopyrum within all of the studied taxa. Uni-cellular non-glandular trichomes were found in Abeliophyllum and three Forsythia taxa (F. europaea, F. giraldiana, and F. japonica). All features were compared and the vascular patterns of the petiole were distinguished in two types: Type 1A: Trace continuous arc - without crystals (Abeliophyllum, Forsythia), 1B: with crystals (Myxopyrum), Type 2: Trace invaginating at ends with crystals (Fontanesia). A detailed anatomical description of the studied taxa is provided, and its systematic importance is also briefly discussed. In conclusion, some petiole anatomical characteristics (e.g., the main vascular patterns, the presence/absence of crystals) can be useful for diagnostic features as well as partly for supporting the recently proposed molecular phylogeny.
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