Species of Dracaena have a secondary thickening meristem in their trunk, termed Dracaenoid thickening by some authors,[citation needed] which is quite different from the thickening meristem found in dicotyledonous plants. This characteristic is shared with members of the Agavoideae and Xanthorrhoeoideae among other members of the Asparagales. Dracaena species can be classified in two growth types: treelike dracaenas (Dracaena fragrans, Dracaena draco, Dracaena cinnabari), which have aboveground stems with a single cluster of leaves at the end of each stem and rhizomatous dracaenas (Dracaena trifasciata, Dracaena angolensis), which have underground rhizomes and leaves on the surface (ranging from straplike and moderately thin to thick and cylindrical). Many species of Dracaena are kept as houseplants due to tolerance of lower light and sparse watering