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Alnus maritima and Alnus serrulata are riparian shrubs that occur in similar habitats in the southern and eastern United States. Alnus serrulata is abundant throughout this range, but A. maritima is rare, occurring only in small populations in Oklahoma and Georgia and on the Delmarva Peninsula. Alnus maritima is more resistant than A. serrulata to water and temperature stresses, but the degree to which insolation influences the restricted distribution of A. maritima is unknown. Our goals were to characterize the shade tolerance of A. maritima and A. serrulata and determine whether differences in shade tolerance could help explain the differing ecological success of the two species. Measurements in nature showed that leaves of A. serrulata have greater concentrations of chlorophyll than do leaves of A. maritima, and a greater percentage of A. serrulata inhabit shaded sites. Two experiments evaluating the resistance of seedlings to light‐deficit stress revealed that A. maritima had a greater photosynthetic ...

We conducted a population genetic analysis of the heterocarpic species Heterotheca subaxillaris (Asteraceae, camphorweed) to determine whether there are mating system and, consequently, genotypic differences between ray and disc achene pools that correspond to ecological differences between achene morphs. No significant differences in levels of genetic diversity were detected between ray and disc achene pools of H. subaxillaris. A mixed mating system was measured overall ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $tm_{\mat...

Dimorphic ray and disc achenes of Prionopsis ciliata (Asteraceae) were compared to determine whether ecological and genetic differences exist that correspond to structural differences between achene morphs. Ray achenes were significantly heavier and took a significantly longer time to germinate than disc achenes, which is indicative of differing dispersal and demographic functions between achene morphs. Significant heterozygote deficiency was detected in ray and disc achene seed pools. Mean observed heterozygosity across all populations and within two populations was significantly greater in the disc achene pool than in the ray achene pool. FIT and FIS were significantly higher and GST was significantly lower in the ray achene pool than the disc achene pool. Overall, ray and disc florets were predominantly self‐fertilized. Significant differences in outcrossing rates were detected between ray and disc florets within five populations. The results do not indicate a clear relationship between ecological func...

Androecium development and gynoecium development were compared among hermaphroditic flowers from nonfruiting (NF) and low-fruiting (LF) trees and female flowers from high-fruiting (HF) trees of gynodioecious Ocotea tenera Mez & J.D. Smith ex Mez. Dramatic qualitative differences in androecium development were identified between gender classes. Anthers in all flowers initiated microsporogenesis, with flowers from NF and LF trees eventually producing pollen, although some pollen from LF trees was slightly malformed. In anthers from HF trees, pollen development terminated after microspore tetrads developed, and the immature pollen grains eventually degenerated. Allometric relationships between flower growth and gynoecium growth differed among gender classes, with flowers from HF trees having a significantly greater slope. Allometric relationships between androecium and whole-flower growth were not different, but androecium size was reduced in female flowers. We argue that the gene, or genes, causing abortion...