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Accueil du site → Doctorat → Royaume-Uni → 1991 → Zygaphyllaceae : anatomy, taxonomy, and some aspects of physiology

University of London (1991)

Zygaphyllaceae : anatomy, taxonomy, and some aspects of physiology

Sheahan, M.P.C

Titre : Zygaphyllaceae : anatomy, taxonomy, and some aspects of physiology

Auteur : Sheahan, M.P.C

Université de soutenance : University of London

Grade : Doctor of Philosophy (PhD) 1991

The Zygophyllaceae are a heterogeneous family of semi-desert and Mediterranean plants which grow in arid and saline areas throughout the tropics and subtropics. Sixteen genera and thirty-six species of the family were grown for anatomical and physiological examination. Leaf and stem parts were examined by light microscopy and scanning electron microscopy ; a morphological and anatomical description is provided for each species, with a discussion of special points of interest such as root nodules, pulvini, and mucilage and tannin cells. The anatomical findings are discussed in relation to strategies for survival in the seasonally water-limited habitats of these plants. There was much plasticity in the anatomy. The majority of the species studied were characterised by fleshy leaves with thin cuticles, scanty sclerenchyma, water storage tissue, and abundant crystals. Anatomical aspects of the plants with C4 metabolism were of special interest ; so were mesophyll arrangement, vein density, tracheoidal idioblasts accompanying the veinlet terminations, and trichomes. Plants were tested for their CO2 compensation point, and it was found that two genera (Tribulus and Kallstroemia) have compensation points consistent with the C4 pathway of phtosynthesis, as did one member of the type genus Zygophyllum, Z. simplex. Some succulent members of the family were also tested for CAM activity, but with negative results. Some investigation of germination and early growth in saline conditions was undertaken with two halophytic species, which were found to be intolerant of high salt concentrations at the germination and early seedling stage. Finally the phylogenetic relationships and current classifications of the family are examined in the light of the anatomical and physiological findings. Some general (Peganum and Malacocarpus, Nitraria, and Balanites) have anatomical characters which set them apart from the rest of the family : this is in accordance with other analyses of the family based on morphological, palynological and biochemical studies.

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