Possible Clues:

• It provides flavour in salads or relishes
• Weed - colour of horse
• Equine color
• Plant grievously spreading across river and lake
• Herb and horse
• Reddish-brown horse; edible plant
• Edible plant, horse of light reddish-brown coat
• Horse
• Plant doubler, perhaps, in a sole saucy way
• The sort of horse that might be planted on 31 across