Opuntia humifusa late spring. The juicy and edible red fruits measure from 3–5 cm. As the fruit matures, it changes colour from green to red, and often remains on the cactus until the following spring. There are 6 to 33 small, flat, light-colored seeds in each fruit. This species was originally native to arid areas of Montana southward to New Mexico, and eastward to the lower Great Lakes, and along the East Coast from the Florida Keys to coastal Connecticut. Some botanists treat this cactus as a variety of "Opuntia compressa": hence "Opuntia compressa" var. "humifusa", or a synonym of "Opuntia compressa".
Plant functional type key parameters are defined, such as fecundity, competitiveness, resorption (rate at which plant decays and returns nutrients to the soil after death), etc.; the value of each parameter is determined or inferred from observable characteristics such as plant height, leaf area, etc. Climatologists and ecologists struggle to determine which minimal set of plant characteristics best model the actual responses of the biosphere in response to climate changes. Plant functional type Plant functional types (PFTs) is a system used by climatologists to classify plants according to their physical, phylogenetic and phenological characteristics as part of an overall effort to develop a