The flowers they produce are often blue or purple and as soon as the seed is set, the plants wither and die.[3] About two thirds of the plant species are annuals with smaller numbers of perennial plants, shrubs and sub-shrubs. The native flora is in transition between semi-desert and desert vegetation and is of importance in the study of how humans are impacting semi-desert habitats. The aftermath of the Gulf War and the inundation of much of the land with hydrocarbon residues has caused considerable damage to the soil structure and considerable changes to the environment.[4] Date palms have been planted at oases and near the coast and mangroves and sea grasses grow on the mudflats near Kuwait Bay, their roots helping to stabilise the coastline.[3]