CRAWFORD, PHILLIP T* and WAYNE J. ELISENS. Dept. of Botany and Microbiology, University of Oklahoma, Norman, OK 73019. - Systematics of native North American Linaria (Scrophulariaceae).
The native North American toadflaxes (Linaria section
Leptoplectron) comprise a morphologically-variable complex of
taxa that have been collectively recognized as a distinct genus
(Nuttallanthus D. Sutton) and individually assigned to specific
and varietal rank. Linaria canadensis and L. texana are
locally abundant in sandy soils throughout much of temperate North
America; L. floridana is confined primarily to Atlantic and
Gulf coastal areas where all three taxa occur occasionally in dense,
mixed populations. These plants produce cleistogamous flowers early in
the growing season; showy, fragrant chasmogamous flowers appear later
and attract numerous Lepidopteran and Hemipteran visitors. Chromosome
counts reveal no variation in ploidy level within the complex. Field
and greenhouse breeding-system studies indicate high levels of
self-fertilization: all individuals studied were entirely
self-compatible and many “chasmogamous” flowers selfed prior to
anthesis; pollen is required for seed production. While hand-performed
cross pollinations between plants within each taxonomic group resulted
in reduced seed set (possibly due to limited pollen transfer), no
intertaxon hand-pollinations produced viable seeds. Field tests
conducted in several populations of L. texana involved five
treatments: open pollination, pollinator exclusion, floral
emasculation and pollinator exclusion, emasculation and
open-pollination, and hand/self-pollination of emasculated flowers.
These tests indicate L. texana is facultatively xenogamous;
while many potential pollinators were observed visiting successive
flowers, successful pollen transfer and seed set was rare. These
results are consistent with an analysis of isozyme variation, which
revealed low levels of observed heterozygosity and infrapopulation
genetic polymorphism throughout the complex. Analyses of morphological
and genetic variation within and among 50 populations of Linaria
canadensis, L. texana and L. floridana yield broadly
consistent results and suggest that these taxa should be recognized as
distinct species. Phenetic analyses identify numerous quantitative and
qualitative morphological differences among these taxa; isozyme data
indicate that these taxa are reproductively isolated in areas of
sympatry.
Key words: breeding system, isozymes, Linaria, morphology, Nuttallanthus