A foundation monograph of Ipomoea (Convolvulaceae) in the New World

Underground parts
Although annual species are generally known to have fibrous roots, little reliable information is available about most of the perennial species. Erect species of the cerrado nearly always arise from a woody xylopodium but this is known to vary considerably in form and development from species to species. Ipomoea hirsutissima, for example, has very large somewhat woody tuberous roots. Similar storage roots are seen in other species in Clade A1 including I. lilloana (Figure 15D) and I. opulifolia (Figure 15E). The best-known species for its tuberous rootstock is, of course, the edible I. batatas, but storage roots occur in many different clades throughout the genus, such as I. bonariensis and I. platensis in Clade A2, this last sometimes cultivated as a succulent. Those of I. pubescens and I. plummerae in Clade B are sometimes eaten, while those of I. pandurata and I. leptophylla in Clade C are noted for their size. Other species have tubers which can be used medicinally, notably I. purga and I. jalapa. However, for the vast majority of species there is no accurate information about their rootstock. Although this character may prove to be of economic importance in the future and is significant in discussions around the origin of the sweet potato (Muñoz-Rodríguez et al. 2019), it can be little used at the present time in species delimitation.
Latex
White latex is recorded as present in many species and is sometimes abundant, notably in trees and lianas, including species in the Arborescens and Calonyction Clades as well as in the aptly named Ipomoea lactifera. However, its presence often goes unrecorded and it may be more or less obvious according to climatic conditions.
Stem
Stems may be entirely herbaceous, woody in the lower parts and herbaceous above, or entirely woody except for the new growth. Stems may be glabrous or variously hirsute, the indumentum usually being similar to that of the peduncles, petioles and leaves, especially the abaxial surface of the leaves. There is a tendency for older stems to be somewhat glabrescent. Unusual features of the stem include distinct wings (Ipomoea pterocaulis, I. splendor-sylvae, I. subalata, I. kahloae), squamose dark glands (I. balioclada), warty protuberances (I. verruculosa, I. tuboides), spinules (I. spinulifera), soft spines (I. setosa), soft fleshy teeth (I. muricata, I. alba, I. parasitica) and granulose protuberances (I. granulosa).