Morphology and development of floral shoots and organs in certain Zannichelliaeeae

Development of reproductive shoots and associated organs in Vleisia aschersoniana, Althenia filiformis, Lepilaena bilocularis and L. cylindrocarpa (Zannichelliaeeae, sensu Dumortier) has been examined using an epi-illumination technique to provide photographic documentation. Floral shoots share a similar basic developmental pattern. The vegetative shoot is terminated by a unisexual flower, but growth is continued from the axils of leaves immediately below so that fairly regular sympodia develop. Vleisia is most variable in the expression of this pattern. The flowers are simple, consisting of a single stamen or three carpels (one in Vleisia) and show marked similarity in development. Short scale-like appendages, reminiscent of a perianth, develop at the base of the stamen in Althenia and Lepilaena. An outgrowth at the tip of the connective in Lepilaena bilocularis and two at its middle part in Vleisia are initiated at late stages of stamen development. Carpels are subtended by membranous tepal-like appendages that are initiated at the same time as the carpel primordia. Each carpel primordium becomes peltate and develops a bitegmic ovule on the adaxial portion of the carpel wall which in turn overgrows the ovule and ultimately forms a long thin style with either a funnel-shaped (Vleisia, L. cylindrocarpa) , peltate (L. bilocularis) or feathery (Althenia) stigma. Relationships with other Alismatales are discussed.     

Assessing and predicting the success of Najas flexilis (Willd.) Rostk. & Schmidt, a rare European aquatic macrophyte, in relation to lake environmental conditions

Najas flexilis (Willd.) Rostk. & Schmidt is a submerged annual macrophyte, rare in Europe, which is protected under the EC Habitats Directive. N. flexilis appears to be decreasing in the British Isles, its main stronghold in Europe. We outline the environmental conditions required for N. flexilis growth, comparing between present and recently extinct sites for the plant. Plant traits (leaf area/shoot length; and reproductive number/shoot length) can be used to assess N. flexilis population success, and models are produced that can predict this. Both the comparison between present and extinct sites, and the models, suggest that eutrophication and acidification of lakes are the main threats to N. flexilis. Acidification appears to reduce the ability of N. flexilis to produce seeds (potentially fatal for an annual). On the other hand, eutrophication leads to conditions where N. flexilis, an obligate carbon dioxide utiliser, cannot photosynthesise due to the predominance of bicarbonate rather than dissolved carbon dioxide in lake water.