Vegetative Anatomy of the Haemodoraceae and Its Phylogenetic Significance

Abstract

Premise of research. Haemodoraceae are a relatively small monocot family consisting of 14 genera and approximately 108 species and are distributed in parts of Australia, southern Africa, South and Central America, and eastern North America. The family is divided into two subfamilies, Haemodoroideae and Conostylidoideae. This research focuses on the vegetative anatomy of the family, with an emphasis on leaf anatomical features. The aims of this project are (1) to acquire new vegetative anatomical data for a large selection of Haemodoraceae and (2) to evaluate these data in the context of both phylogenetic relationships and environmental factors.Methodology. Cross sections of roots, stems (scapes), or leaves of 60 species and 63 ranked taxa from all 14 genera of the family were prepared and stained using standard histological methods, and SEMs were made of the leaf surface. Line drawings were prepared of leaf cross sections of an exemplar of each genus. Tissues and cells were examined and photographed, and comparisons were made among taxa. For leaf epidermal cells, the ratio of cell wall transectional area∶cell transectional area was calculated and plotted. Several discrete anatomical characters and character states were defined and plotted on a recently derived cladogram and examined for phylogenetic signal. Correlation of certain anatomical features with environmental factors was also noted.Pivotal results. Leaf anatomy provides several phylogenetically informative traits, including bulliform cells, tannin cells, marginal fiber caps, the relative wall transectional area of epidermal cells, the morphology of palisade cells, the distribution of fibers in the vascular bundle, leaf aerenchyma, mucilage cells, and silica bodies. These features generally correlate significantly with the pattern of phylogenetic relationships in the family. Silica cells, tannin cells, and mucilage cells, all of which may function to deter herbivory, are generally restricted to particular clades. The relative epidermal wall thickness of members of the genus Conostylis is significantly higher than in other members of the family, a feature that may represent an adaptation to their hot, dry environments.Conclusions. The systematic and ecological value of studying plant vegetative anatomy is supported by this study. Vegetative anatomical features of the Haemodoraceae show considerable and significant variation. Numerous anatomical features exhibit a high phylogenetic signal and are apomorphic for specific clades. Some anatomical features are possible adaptations to habitat, climate, or herbivory. However, quantifiable ecological data are needed in future studies for assessing the adaptive significance of these anatomical features.