Final answer:
Bermudagrass has the greatest heat hardiness among the grass species listed, thanks to its drought-resistance and ability to thrive in hot conditions.
Step-by-step explanation:
The heat hardiness of grass species is a measure of their ability to withstand high temperatures. Among the grass species listed, C. bermudagrass is known to have the greatest heat hardiness. This species is highly drought-resistant, making it capable of thriving in hot weather conditions, unlike some other species that may struggle.
While zoysiagrass, buffalograss, and St. Augustinegrass also perform well in warm climates to some extent, bermudagrass is particularly reliable due to its deep root system and quick recovery from stress. Therefore, under extreme heat, bermudagrass would typically outperform the other grasses in maintaining health and appearance.