Cuphea Species and Cultivars Differ in Occurrence of Intumescence

Cuphea (Cuphea spp.) are herbaceous ornamental plants that are being more widely produced in greenhouses because of their unique flower morphology, profuse flowering, and ability to perform well in heat and drought in the landscape. However, some species and cultivars are susceptible to intumescence, a physiological disorder characterized by abnormal cellular outgrowths on the leaf surface. In severe cases, the leaves are nearly completely covered with the outgrowths, and leaves begin to curl, resulting in unsalable plants. With many recent cuphea introductions, we conducted a screening trial of 23 ornamental cuphea species and cultivars to document intumescence occurrence and severity, and to characterize plant growth habit, floral characteristics, and leaf morphology. Two different groups of plants were grown in a glass greenhouse under polyethylene with UV-block for six weeks. Plants were replicated across six blocks with three pots per experimental unit that allowed for destructive evaluation of one pot per experiment unit every two weeks. Plants were rated based on overall intumescence using a scale from 0 to 5 (0= no intumescence and 5 = severe) and % leaves with intumescence. In the first group (4 February through 16 March), only four out the 11 cultivars developed intumescence. Intumescences were observed within two weeks of initiating the study, and severity increased throughout the study for those that developed intumescences. Intumescence was most severe on C. llavea selections, including ‘Flamenco Samba’ and ‘Tiny Mice’, in which average plant ratings were between 4 and 5 after four weeks. In the second group of 12 cultivars (8 March through 20 April), intumescence was observed on four cultivars, including three different Sriracha™ selections and ‘Georgia Scarlet.’ Similar to the responsive cultivars in the first group, the cultivars that developed intumescence in the second group were also C. llavea hybrids. These results will aid greenhouse growers in selecting cuphea varieties for production that do not develop intumescence if they are produced in a UV-deficient protected environment.