02457nas a2200157   4500008004100000245003500041210003500076260002100111300001000132520196200142653008302104100002102187700002202208700001902230856005002249       2000                        eng d00aModularity in helobial flowers0 aModularity in helobial flowers  aMelbournebCSIRO  a63-743 aWe have previously proposed that the flowers of helobial monocotyledons are derived from assemblages of primitive unisexual units. The main reason for the proposal lies in the different and partly independent developmental patterns of the periath/androecial and the gynoecial components of the flower. In many cases in the Zosterales, e.g. Triglochin, Lilaea, Potamogeton, and Scheuchzeria, there is stamen/tepal superposition: each stamen is formed above a perianth member in a way suggesting an axillary relationship, and the set of organs occur in whorls of different numbers according to the taxon. Similarly, in the Alismataceae and related families, the perianth members occur in whorls of three, and there is commonly an association between a petal and a superposed pair of stamens which develop in association with it, often from what appears to be a common primordium. Further stamens may be initiated above (some Alismataceae) or below (Hydrocleis) the firstformed stamens. In all these cases carpels are initiated in what seems initially to be a whorled pattern above the androecium, with the  numbers in a whorl corresponding to those in the perianth. However, it has been shown in Potamogeton and Ruppia that carpel positioning is more flexible and appears to operate like an ordinary phyllotactic system. The flowers can be seen as being made up of two different types of module, one being the perianth/stamen complex, and the other the carpel. We now have additional data for floral development in two genera of Alismataceae, Luronium and Wiesneria, which complement older data and seem to reinforce the concept of independence of development in the two regions. Phylogenetic analysis indicates these genera are in interesting position within Alismataceae: Luronium is near other genera showing some range of gynoecial organisation, and Wiesneria is part of a complex including Sagittaria which shows extreme variation in meristic complexity.10aHelobial, flowers, development, evolution, Alismatidae, Alismataceae, monocots1 aPosluszny, Usher1 aCharlton, Alan, W1 aLes, Donald, H  uhttps://juncaginaceae.myspecies.info/node/28602388nas a2200133   4500008004100000245013300041210006900174300001200243490000700255520182900262653009202091100002102183856005002204       1983                        eng d00aRe-evaluation of certain key relationships in the Alismatidae: floral organogenesis of Scheuchzeria palustris (Scheuchzeriaceae)0 aReevaluation of certain key relationships in the Alismatidae flo  a925-9330 v703 aTransition to flowering in the North-temperate bog plant Scheuchzeria palustris occurs in early May and results in the formation of a simple raceme with six flowers. Five of the flowers are subtended by large foliar bracts, while the sixth and last-formed flower on the inflorescence remains ebracteate. The individual flowers develop along a clearly trimerous pattern. The three outer tepals develop first, arising almost simultaneously at the periphery of the triangular floral apex. They are followed closely by the development of the three anti-tepalous outer stamens. The three inner tepals are next in the developmental sequence, alternating with the outer whorl of tepal-stamen pairs but arising at a slightly higher level on the floral meristem. Three inner stamens are initiated opposite the inner tepal primordia. Finally, three gynoecial primordia are initiated on the remaining central portion of the floral apex and alternating with the inner whorl of tepal-stamen pairs. Each carpel develops at first as a horseshoe-shaped structure. Two ovules form in each carpel, initiating on the adaxial margin of the carpel wall. Histogenesis of all floral appendages involves initially periclinal divisions in the second tunica layer followed by corresponding anticlinal divisions in the first tunica layer and concurrent activity in the underlying corpus. Separate procambial strands differentiate acropetally from the inflorescence axis to each tepal-stamen pair and then bifurcate. The vascular connection to the gynoecium develops directly from the strands in the tepal-stamen pairs. The results of this developmental study of the flower of S. palustris have a significant bearing on the positioning of this and related taxa within the Alismatidae and on the speculation of the phylogeny of the monocotyledon flower.10afloral development, floral organogenesis, Alismatidae, Scheuchzeria, Triglochin, Lilaea1 aPosluszny, Usher  uhttps://juncaginaceae.myspecies.info/node/283