Echium plantagineum(Boraginaceae)is native of the Mediterranean regions,has been introduced and become widespread within the American continent(North to South),South Africa,New Zealand and Australia.This plant has seed dormancy,aggressively spreads to infest vast areas of predominantly agricultural land and is considered a toxic weed to livestock.The objectives of this research were:(i)to study the morpho-anatomy of the diaspores of E.plantagineum;(ii)to identify the pathway of water uptake;and(iii)to characterize the germination and the seedling.The morpho-anatomical studies were carried out analyzing semi-permanent slides of transverse and longitudinal sections of the fruits,seeds and seedlings.Histological,histochemical and conventional staining techniques by using stereoscopic,optical and scanning electron microscopy were applied.In the diaspores,the water uptake pathway was determined by fast green staining,germination tests were performed and the morpho-anatomy of seedlings was analyzed.The diaspores showed acrescent calyx surrounding the fruit,composed by 4 rough tuberculate mericarpids.Each indehiscent mericarpid encloses an exalbuminous seed with a thin coat and a spatulate embryo with folded coty-ledons.Water uptake took place through the vascular trace“protuberance”in the cicatrix of the mericarpid,which triggers the germination process.Germination was epigeal,the cotyledons were photosynthetically active at the emergence,and a rudimentary developed gemmula was observed.Germination percentage was 66.5%.The macrosclereids of the pericarp functions as an obstacle to water uptake,which is overcome when the mericarpid is detached from the gynobase,and the protuberance that acts as a water uptake path is exposed,leading to germination.The morpho-anatomical characteristics of diaspore,explain the successful dispersal for this aggressive weed,and provide important information in relation to the necessary care for its control.
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