Phlocideae is a newly recognized tribe of Polemoniaceae that reflects generic relationships revealed by recent molecular phylogenetic work. This tribe features several closely related annual and perennial lineages and includes the genera Phlox, Microsteris, Gymnosteris, Leptosiphon, and Linanthus. While the Polemoniaceae has been intensively studied using macromorphological and molecular methods, it has received little attention from anatomists. The nature and degree of anatomical variation in the family is thus largely unknown. The primary goal of this project has been to document the anatomical characteristics of leaves, stems, and flowers in the lineages of Phlocideae, with emphasis on Linanthus and Leptosiphon, and to examine the evolution of those characters using the phylogenetic model provided by molecular data. With few exceptions, species in Phlocideae exhibit bifacially distributed stomata, leaf bundle sheaths composed of large, non-photosynthetic cells, and some degree of stem secondary growth. Less conserved characters, informative intergenerically, include the presence of an abaxial mass of fibers in the central leaf vein (characteristic of Linanthus and some Leptosiphon), the formation of bundle sheath extensions from the central vein to either leaf surface (in Microsteris and Phlox), and the extension of the lignified cells of the central vein into a spine-like leaf tip (Linanthus). Within genera, lineages differ in trichome structure and distribution, degree of leaf mesophyll differentiation into palisade and spongy layers, and cuticular features. Anatomical data support the inclusion in Linanthus of four species previously assigned to Gilia but transferred to Linanthus based on molecular data.

Key words: anatomy, Leptosiphon, Linanthus, Phlocideae