A new species of Passiflora, P telesi- phe, is described in subgenus Decaloba. This spe- cies was discovered as a result of observations on the natural history and foodplants of a butterfly (Heliconius telesiphe-Lepidoptera: Nymphalidae: Heliconiiti), whose young stages were previously unknown. The new species and its herbivore are illustrated. The relationships of P telesiphe to other similar Ecuadorean species of Passiflora are briefly discussed. Herbaceous vine; young stems angulate, minute- ly puberulent, the trichomes ca. 0.5 mm, simple and uniseriate, very slender, drying white; new growth cernuous; stipules 1.5-2.5 mm, linear and somewhat falcate, deciduous, the margins ciliate with trichomes like those of the stems; tendrils ax- illary, minutely puberulent. Leaves with upper sur- face dark green, occasionally variegated with white around the midrib, undersurface dark purple, mi- nutely puberulent on both surfaces, hanging down as if wilted; petiole 1-1.5 cm, glandless, minutely puberulent; blade 3-8 x 5-11 cm, elliptic to ellip- tic lanceolate, with three main veins from the base between which are borne 14-19 ocellate glands, these somewhat pale above, the base acute, the margins entire, the apex three-lobed, each lobe ter- minating in an elongate mucro. New growth leaves and stems purple, changing to green when older. Flowers solitary or more often paired at each node, pendent, with no discernible odor; pedicel 2.5-3 cm, pale burgundy-purplish, minutely puberulent; bracts usually spaced ca. 1.5 mm apart in the distal ? of the pedicel, 7-13 x 2-5 mm, elliptic to ovate, persistent, greenish, tinged purple on live plants, drying brown, the tip long-acuminate, with a few scattered trichomes like those of the stems; buds white, minutely puberulent; sepals 2.0-2.5 cm long, narrowly triangular, membranous, pale green- ish, drying white, minutely puberulent with scat- tered trichomes, reflexed at anthesis; petals 1.0-1.4 cm, narrowly triangular, thin and membranous, white, glabrous, reflexed at anthesis; corona biser- iate, the outer filaments 2.2-2.6 cm, narrowly lig-