Yellow Passionflower (Passiflora lutea)

Passiflora lutea
Flower
Conservation status
Secure (NatureServe)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Malpighiales
Family:	Passifloraceae
Genus:	Passiflora
Species:	P. lutea
Binomial name
Passiflora lutea L.

Passiflora lutea, commonly known as yellow passionflower,^[1] is a flowering perennial vine in the family Passifloraceae, native to the central and eastern United States. The vine has three-lobed leaves and small, yellowish-green, fringed flowers that appear in the summer, followed by green fruit that turn almost black at maturity. It grows in moist to wet habitats.

P. lutea is a perennial, herbaceous, climbing or trailing, unbranched vine that can reach 3–5 m (10–16 ft) in length. Curled, springlike tendrils emerging from leaf axils help the vine to climb on structures or other vegetation. The leaves are trilobed, 3–7 cm (1–3 in) long and 3–15 cm (1–6 in) broad, with a 5 cm (2 in) petiole. Leaves have smooth (entire) margins and are alternate on the stem. The upper surface of the leaves is dark green, and may be mottled with splotches of lighter green.^[2] In the north of its range, it is deciduous.

The showy flowers appear singly or in pairs on slender flower stalks up to 5 cm (2 in) long. Each flower is 1.5–2.5 cm (0.6–1.0 in) wide with narrow yellowish greenish petals and broader green sepals. The fruit is up to 1.5 cm (0.6 in) long and green, turning dark purple or black when ripe.^[3] Each fruit contains up to 10 seeds, which are brown, pointed at each end, and have a textured surface.^[2]

P. lutea is very similar to Passiflora suberosa (corkystem passionflower), differentiated by the leaves, which are more variable and generally have deeper lobes in P. suberosa, and the stems, which are corky or winged in P. suberosa.^[4] Also, P. suberosa has a more limited range, occurring in Texas and Florida and parts of Latin America.^[5] Another similar species is Menispermum canadense (Canadian moonflower), whose leaves are a different shape, with three to seven lobes instead of just three. Also, the fruit of M. canadense grows in clusters and each berry has a single crescent shaped seed.^[3][6]

The genus name Passiflora comes from the Italian word "passio", or suffering, based on an association of the flower parts to the crucifixion of Jesus Christ. The species name luteo is from the Latin word for "yellow", due to the color of the flowers.^[7]

P. lutea is native in the United States from Pennsylvania west to Kansas, and south to Florida and Texas. It is the northernmost species of Passiflora,^[8] occurring slightly further north than P. incarnata,^[9] and tolerant of winter temperatures down to −15 °C, and even −30 °C for short periods.

P. lutea grows in bright shade to sunny places with moist, rich soil, such as open woodlands and low alluvial ground.^[2][7]

Passiflora lutea is considered an endangered species in Pennsylvania.^[10]

Yellow passionflower is often good for butterfly gardens, as it is a host for Julia (Dryas iulia), Mexican and Gulf fritillary butterflies, zebra longwing (Heliconius charithonia) and crimson-patched longwing butterflies.^[11]

The species exhibits complex floral movements typical of the genus Passiflora. Flowers open in the morning and remain open for a single day, during which the reproductive structures shift position. The styles initially point upward but later bend downward (deflex), bringing the stigmas into contact with visiting pollinators and promoting cross-pollination.^[12] However, not all flowers fully complete this movement; some retain upright styles and may function primarily as male flowers.^[12]

Pollination biology varies geographically across the species' range. In central Arkansas, the specialist bee Anthemurgus passiflorae is considered the primary pollinator, frequently contacting both anthers and stigmas while collecting pollen and nectar.^[12] This bee is an oligolectic species that relies almost exclusively on P. lutea for pollen. Other visitors, including wasps, butterflies, flies, and ants, may consume nectar but generally do not contribute significantly to pollination.^[12]

In contrast, populations in other regions such as central Texas are thought to rely more on medium-sized bees (e.g., Bombus, Xylocopa, and Colletes) as pollinators, highlighting substantial geographic variation in pollinator assemblages.^[12]

Passiflora lutea is primarily outcrossing and typically requires animal pollinators for successful fruit production. Experimental studies have shown that fruit set is significantly higher in flowers exposed to pollinators compared to those excluded from insect visitation.^[12] Although generally self-incompatible, the species exhibits low levels of self-compatibility, with a small percentage of flowers capable of producing fruit from self-pollen.^[12]

Fruit set also varies geographically, with some populations exhibiting relatively high reproductive success, suggesting differences in pollinator effectiveness and local ecological conditions.^[12]

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