Possible Clues:

• Rhizome
• Return to gold standard and mint, say
• Rhizome, flower tip as well, rejected by reserve
• Plant onto which another variety is grafted
• Grafting receiver, Eliot's taken to cold castle walls
• Vegetables for the grafter
• Rhizome or tuber initially found in port
• Source of parsnip liquor, perhaps
• Plant grafting component
• Part of plant making radical basis for soup?