Classification of plant based on temperature tolerance

Based on temperature tolerance plants are grouped under 4 categories as follows .
microtherms :plants adapted to low temperature  environments where the temperature in the warmest Month is between 10 degree Celsius and 22 degree celsius in the coldest month it will not fall below 6 degree Celsius. Eg: mixed coniferous forests.
Mesotherms: plants of warm temperate areas where the mean  temperature in the hottest Month is above 22 degrees celsius and in the coldest month not below 6 degree Celsius examples: sub tropical deciduous forests
megatherm: plants of the warmest Tropical environments where  the mean temperature is always above 18 degree Celsius example desert plants, Tropical rainforest .
hekistotherms : cold tolerant plants
Which can resist very low temperatures. example Arctic vegetation and Alpine vegetation.