The fragrant flowers are arranged in crowded heads, spikes, or panicles at the stem tips or axils. Because they are rich in nectar, they attract bees, hummingbirds, and a variety of beetles.
Fruit begins to mature a few months after pollination, and production may be nearly continuous (twice a year in I. feuillei in the Andes). The pods may be flat, twisted, or cylindrical. They are often flattened or four-sided, the margins frequently overhanging. They grow up to 70 cm long and 1–3 cm in diameter, usually with the seeds buried in the white, sweet pulp.
Horticultural Varieties. In pacay, vegetative selections (apparently made in ancient times) exist,10 but no true horticultural varieties are known. As noted, a single selection is of little use in fruit production because of self-incompatibility. Because cuttings establish roots poorly, vegetative propagation has not yet been developed.
Daylength. Pacay is apparently daylength neutral, at least within the subtropics, which in any case are its outer limits.
Rainfall. Pacay requires a subtropical climate with plenty of moisture. At Yurimaguas (Peruvian Amazon), both I. feuillei and I. edulis are very productive (wood, leaf, and fruit) at 1,500–2,700 mm annual rainfall.11
Altitude. Up to 1,500–1,800 m in Peru's inter-Andean valleys.
Low Temperature. Most species are damaged by low temperatures and killed by extended freezing weather.12
High Temperature. Pacay thrives at 25°C; and, with sufficient moisture, seems capable of withstanding short periods above 33°C.
Soil Type. These trees are apparently widely adaptable. They withstand soils from pH 4.0 to 8.0. They tolerate high aluminum saturation (70–90 percent) in acid soils. I. edulis and I. feuillei nodulate profusely even at pH 4.5 and are also heavily mycorrhizal (vesicular arbuscular mycorrhizae). These mycorrhizae play an important role in enabling ingas to take up phosphorus even though phosphorus is in very short supply in acid soils.
Some are reported to exhibit tolerance to waterlogging and are