Place sugar and water in a saucepan and heat slowly until dissolved. Prepare rind from lemon and add to pan. When sugar is dissolved, increase heat and bring to boil. Boil for 10 minutes until reduced and a heavy syrup is formed. Remove from heat. Top and tail rhubarb. Cut into 5cm lengths - if rhubarb is young, leave pink skins on. Remove older skins which may be tough. Add rhubarb and sweet cicely to sugar syrup, pour into a non-metallic bowl and leave to cool. Preheat oven to 220C/425F/gas 7. Remove rhubarb from syrup using a slotted spoon. Pat dry with absorbent kitchen paper. Save syrup. Melt butter. Lay one sheet of filo on work surface and brush with melted butter. Cut sheet in half lengthways. Sprinkle one piece with icing sugar, then top with remaining piece. Dredge with sugar again. Turn pastry with short side towards you. Place some rhubarb on pastry, about 4cm from base and fold pastry up to cover rhubarb. Fold sides and edges in over fruit, then roll up to form a spring roll shape. Place on a baking sheet. Repeat to make six strudels. Brush strudels with remaining butter and dredge with icing sugar. Bake in preheated oven for 12 minutes, until crisp. To serve, cut ends off strudels obliquely to show filling. Serve with rhubarb syrup and decorate with small leaves or flowers of sweet cicely.