MCDILL, JOSHUA R.1*, ROBERT W. PATTERSON1, and J. MARK PORTER2. 1Department of Biology, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132; 2Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, CA 91711. - A comparative anatomical study of Linanthus and related genera (Polemoniaceae), with implications for their relationships and evolution.
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