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

Indumentum
Species may be glabrous or variously hirsute. There is a good deal of intra-species variation and this has often proved to be an unsatisfactory character in species delimitation. Many species or varieties have been recognized over the years based on the presence or absence of hairs and have subsequently been abandoned. Despite this important proviso, many species have a characteristic indumentum which is readily recognized. Species which are always glabrous in their vegetative parts form a long list, as do those which are characteristically sericeous or tomentose. A sericeous indumentum is characteristic of almost all species previously placed in Argyreia, Rivea, Turbina and Stictocardia as well as many that have always been included in Ipomoea. Some unusual indumentum types include:
• Stellate hairs. These are characteristic of certain species notably Ipomoea bonariensis from South America, I. scopulorum from Mexico and I. luteoviridis from Hispaniola. In cases where they are mixed with simple hairs they may be very difficult to observe and pass unnoticed. They are also characteristic of the Astripomoea Clade, which is restricted to Africa.
• T-shaped hairs. Ipomoea malpighipila was named on the basis of the presence of T-shaped hairs. They are not reported from other species, except the related I. aemilii, and are difficult to observe even in these species.
• Scattered long fine hairs. Ipomoea clavata, I. dolichopoda.
• Density and appearance. Many species are densely hairy especially on young stems and the abaxial surface of leaves but sometimes on all vegetative parts. Where hairs are dense the leaves are often white or grey in colour and characteristic of the species. This kind of indumentum is not always easy to define and is sometimes described as canescent, sericeous, tomentellous, tomentose or densely pubescent by different authors.
• Gland dots. Distinct gland dots are found in some species, especially on the abaxial leaf surface but sometimes on other vegetative parts or even the corolla. They usually appear as dark dots and are so characteristic of I. tiliifolia that they are often regarded as a defining characterstic of the Stictocardia Clade (Austin and Demissew 1997). They occur sporadically elsewhere as in some specimens of I. megapotamica, I. reticulata and I. batatoides. As white dots they are characteristic of I. eremnobrocha and the related species I. isthmica and I. peteri.