Variation in fiber cables in the lacunae of leaves in hybrid swarms of Typha × glauca

• Fiber cables in leaves of flowering plants of Typha are a diagnostic character.
• Fiber cables are present in all leaves of T. angustifolia.
• Fiber cables are absent in the last formed leaves of flowering T. latifolia.
• Fiber cables are variable in flowering individuals of T. × glauca.
• Fiber cables can be used to weigh affinities of T. × glauca and the parental species

The presence or absence of fiber cables in the lacunae of the last formed leaf blades of flowering Typha plants is a diagnostic character. The fiber cables are present in all leaves of Typha angustifolia L., but are absent in the last formed leaves of Typha latifolia L. We find great variation in the presence of fiber cables in the last formed leaves of individuals in stands of Typha × glauca Godr. (pro sp.). We find that individuals that comprise the hybrid swarms that are closer to T. angustifolia in terms of standard characters have fiber cables in most or all of the last formed leaf blades before the inflorescence. By contrast, those individuals closer to T. latifolia in terms of standard characters do not have fiber cables in the last formed leaves before the inflorescence. The lengths of the longest fiber cables are correlated with the lengths of the leaves in T. angustifolia and the “angustifolioid” T. × glauca, but not in T. latifolia and the “latifolioid” T. × glauca. The variability in the taxonomically, morphologically and biomechanically-significant fiber cables in the lacunae in reproductive plants may be useful in characterizing and understanding the composition of a Typha stand.