Summary Observations and phenetic analyses of the leaf anatomy of 23 Smilax species from Thailand were carried out to assess the utility of anatomical characters in elucidating the taxonomy of the genus. The outline of the petiole in transverse section is circular or elliptic. The abaxial outline of the midrib is rounded, acute or attenuate. Parenchymatous, sclerenchymatous and sclereid cells are observed in ground tissues. Th...

Summary Two new species, Justicia flavescens and J. vasculosoides are described and illustrated from northern Thailand. Both species have restricted distributions. The conservation status of each species is assessed.