1. Passiflora L. (passion flower)

Plants herbaceous perennial vines, with axillary tendrils. Leaves alternate, simple, palmately lobed. Stipules scalelike or more commonly herbaceous, inconspicuous. Extrafloral nectar glands present on the petioles of some species. Inflorescences axillary, the flowers solitary or often in pairs. Flowers actinomorphic, perfect, perigynous, with a saucer-shaped to cup-shaped hypanthium. Sepals 5, free, spreading to somewhat reflexed, attached to the rim of the hypanthium, petaloid or green on the outer surface and colored on the inner surface. Petals 5, free spreading to somewhat reflexed, attached to the rim of the hypanthium, usually brightly colored. Conspicuous corona present between the petals and stamens, this structurally complex, of filamentous and/or membranous appendages, and often brightly colored. Stamens and pistil attached to the tip of a noticeable central stalk (known as the androgynophore, an extension of the receptacle). Stamens 5, inserted at base of ovary, the anthers attached toward the midpoint, pendant. Pistil 1 per flower, composed of 3 fused carpels, with 1 locule and numerous ovules, the placentation parietal. Styles 3, elongate, spreading to somewhat pendant, the stigmas capitate. Fruits berries, the seeds surrounded by a pulpy aril. About 500 species, mostly in tropical and warm-temperate regions of the New World.

The common name refers to the imaginative correlation of the flower parts with components of the Christian crucifixion rite, or Passion of Christ, in a period when the Doctrine of Signatures was an accepted philosophy (Vanderplank, 2000). The corona represents the crown of thorns, including a fringe of blood. The 10 perianth segments represent the 10 faithful apostles. The 3 stigmas represent the Trinity or nails, and the 5 stamens correspond to the 5 wounds. The tendrils might represent whips or ropes. Doctrine of Signatures refers to the medieval European philosophy of cosmology and herbalism in which the “essential virtues” or “purpose” of living things could be inferred through interpretation of selected morphological features in light of superficial similarities with medical, religious, or other themes.

Passiflora exhibits a wide range of flower morphologies (Brizicky, 1961; MacDougal, 1994). In bee-pollinated species, the corona acts as a landing platform and the concentric bands of purple guide the bee to the relatively concentrated (40% sugar) nectar, which is secreted by a glandular ring at the base of the androgynophore into the cup-shaped hypanthium. The corona forces the bee to probe around the flower to get the nectar. The anthers are in position to brush against the insect’s body, and move away after pollen release. The styles then curve downward and position themselves where they will brush against a bee carrying pollen from another plant. The flowers open in the morning and last only one day. In the tropics, flowers pollinated by hummingbirds are characterized by having a red color, small corona, and elevated androgynophore. Pollination by bats or wasps also occurs in a few species.

In the tropics, the leaves of Passiflora are eaten by herbivorous insects, notably Heliconius butterflies, and the plants have developed a number of chemical and morphological defensive mechanisms in a kind of coevolutionary “arms race” (W. W. Benson et al., 1975; Gilbert, 1982). The extrafloral nectaries on the leaf petioles attract ants, which in turn protect the plant from herbivores (McLain, 1983).

Many species are used as ornamentals and several species are grown commercially for their edible fruits,which are eaten fresh or pressed for juice. Although once considered close to the Cucurbitaceae because of their tendrils and parietal placentation, recent molecular studies indicate that the Passifloraceae are instead related to Turneraceae, Violaceae, Flacourtiaceae, and Salicaceae.