Original paper

Morphology of Thelethylax isalensis (Perr.) C. Cusset (Podostemaceae Podostemoideae)

Jäger-Zürn, Irmgard

Abstract

Vegetative and floriferous root-borne shoots of the aquatic and rocky river beds inhabiting Thelethylax isalensis are sessile and foliated with long subulate leaves, and differ by the lack of the characteristic shoot dimorphism from the two other species of the genus. In spite of the strongly different appearance, T. isalensis shares an exceptional feature with T. minutiflora and T. insolata: the position of floral organs within the typical “Podostemum-flower”. In this type of flower, the androphore with one or more stamens arise at the side of the ovary, commonly in decussate position relative to the distichous foliation of the floriferous shoot. In T. isalensis, however, the androphore with the two stamens as well as the two carpels of the ovary, arise in the same distichous phyllotaxic order as foliage leaves; floral organs are not decussately, but in one row distichously positioned. The three species of Thelethylax contrast in this synapomorphic feature to all other species with “Podostemum-flowers”. The resemblance of T. isalensis to Asian species, the infrageneric similarity and character evolution in the genus are discussed.

Keywords

evolutioninfrageneric similarity“podostemum-flower”position