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Extrafloral nectaries
These have been reported in many species including Ipomoea alba, I. batatas, I. bonariensis, I. carnea, I. indica, I. leptophylla, I. mauritiana, I. muricata, I. pes-caprae and I. tuboides (Keeler 1977, 1980, 1985, Keeler and Kaul 1979, Mondal et al. 2013, Meeuse and Welman 2000). These are usually found on the petioles, at the base of the leaf where it joins the petiole or on the sepals. It is postulated that they attract ants which help to protect the plant from predators. However, they are not readily observed and their taxonomic value is uncertain as they are not necessarily constant in a particular species (for an example, see the discussion about I. indica in Keeler (1985). The case of I. tuboides is particularly interesting as there are no native ants in Hawaii, suggesting perhaps that the nectaries evolved in the ancestor of this species before it was dispersed to Hawaii from the American mainland.
Leaves
Leaves are exstipulate but a few species have pseudo-stipules (notably Ipomoea cairica, I. fissifolia and I. quamoclit), formed by modified leaves or prophylls. Leaf size can be distinctive but difficult to quantify diagnostically. Large leaves are a feature of a few species such as Ipomoea ampullacea, I. magnifolia and I. philomega whereas small leaves are characteristic of many annual species but also of some perennials such as I. hartwegii and I. rupicola.
Leaf shape is mostly related to habit with almost all climbing species having ovate to deltoid leaves with a truncate, cordate or sagittate base. Elliptic leaves are rare and mostly found in trailing species. Lanceolate, oblong or oblong-elliptic leaves are mostly a feature of erect species. Some unusual shapes occur, such as the strap-shaped leaves of I. tenuissima.
Leaves may be entire or variously divided. Pinnate leaves are only present in Ipomoea quamoclit, and pinnatifid to lyrate-dentate leaves in a few Mexican species (I. ancisa, I. sescossiana, I. tacambarensis, I. stans). A much larger number of species have leaves palmately lobed. The number of lobes, usually 3 or 5, occasionally more, and the depth of lobing are often characteristic of a particular species. However, leaf lobing is often an inconstant character, many species having entire-leaved forms or forms that intergrade with the normally lobed forms. The leaves of some, such as I. bonariensis, I. clausa, I. microdactyla or I. mauritiana are notoriously variable in form. A relatively small number of species have leaves palmately divided into separate leaflets and this character is usually constant. Species which present forms with both lobed leaves and leaves divided into separate leaflets occur in only a very few species (I. cairica, I. bonariensis, I. homotrichoidea).
The leaf base is sometimes distinctive, particularly in those species that have leaves with strongly cordate or strongly cuneate bases. Sagittate or hastate leaves are also often distinct but may intergrade with the more common cordate leaf base. Rounded leaf bases often intergrade with shallowly cordate or truncate leaf bases and are difficult to characterize.
The leaf margins are usually entire to slightly undulate but a few species have distinctly dentate leaves (I. odontophylla, I. schaffneri, I. noctuliflora, I. ignava, I. peruviana, I. descolei and I. erosa). A few species may have 1–several rather large teeth on the margins, usually towards the base (I. acanthocarpa, I. dumetorum, I. eriocalyx). In the majority of species the leaf apex is acute to acuminate, although the actual tip may be somewhat obtuse. The tips are commonly mucronate but in a few cases the midrib extends as a mucro several millimetres in length (I. walteri). In a few species the apex is distinctly retuse (I. pes-caprae).
In general, petiole length is of little significance except that short or absent petioles correlate with an erect habit and elongate leaf shape as noted earlier. One curious feature is the fusion of the petiole and the peduncle at least for part of their length (I. connata, I. bracteata, I. dumosa).
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