It turns out this plains m biome is actually the roofed forest m biome.
													
																	Roofed forest m biome id. 
								
	
		
	
																	Main biomes have a numeric id from 0 to 127 while biome variations normally have a numeric id of 128 original biome number. 
																	I just attached the pictures that shows the biome id of the biome. 
																	Renamed mutated roofed forest to dark forest hills. 
																	Biome ids got changed in 1 13. 
															
													
								
	
		
	
																	Roofed forests are biomes that were implemented in the update 1 7 2 along with many others. 
																	Added lily of the valley that can generate in dark forests. 
																	This means this is now a bug report on roofed forest m biomes not generating trees or tallgrass. 
																	Added roofed forests along with many other biomes. 
															
													
								
	
		
	
																	Changed the id roofed forest to dark forest. 
																	Renamed roofed forest m to mutated roofed forest. 
																	Mountain edge deep. 
																	Renamed roofed forest to dark forest. 
															
													
								
	
		
	
																	These biome numbers are used when creating a customized superflat world. 
																	Each type of biome has its own biome id shown in the following table.