Many hybrids and cultivars are known. Several hybrids and cultivars have been developed. These include interspecific hybrids or crosses between different breeds. A great many hybrids, and cultivars, have been produced. Most delphinium hybrids and cultivars are derived from "D. elatum". Many different corn snake hybrids are bred in captivity. Like other inter-species hybrids, mules and hinnies are usually sterile. The Ford demonstration vehicles and Hybrids Plus conversions are similar. Some artificial hybrids are cultivated in gardens. Heterosis is common in both animal and plant hybrids. Captive tigers were bred with lions to create hybrids called liger and tigon. This is most common with plant hybrids. PHEVs typically require deeper battery charging and discharging cycles than conventional hybrids. Two interspecific hybrids, "P". Muckross Gardens are famous for their collection of rhododendrons, hybrids and azaleas, and exotic trees.