The balloon vine is a strongly overgrown, perennial herbaceous
climbing plant that can even become lignified at the base. Growing over 10 meters high, it can bloom at a height of around 25 cm. The slender, grooved stems are hairy bald to sparsely downy. The 5 to 6 cm long, triangular foliage leaves distributed on the stem are divided into a
petiole and
pinnate leaf blade. The petiole is (0.5 to) 1.5 to 3.5 cm long and the
rachis is 0.4 to 2 cm long. The opposite leaflets are 1 to 2 cm long and the terminal leaflets are 4 to 6 cm long. The leaf margins are serrated. The stipules are reduced to tiny, early-falling scales. On the side of a 5 to 9 cm long, sparsely downy hairy
inflorescence stem, there are two 1 mm long bracts, two circularly rolled
tendrils and three to seven flowers in a zymous inflorescence.
Flowers and fruit The functionally
unisexual flowers are
zygomorphic and fourfold double
perianth. Of the four free, concave, durable
sepals, the outer two are circular, 2 mm long and
ciliate, while the inner two are oblong-ovate, 3 to 4 mm long and glabrous. The four white to yellowish petals are
obovate and about 3 mm long, the upper two are each adorned with woolly scales and the lower two have large, leaf-shaped scales and two glands. In the male flowers are two circles with four free stamens each and rudimentary stamps present. The compressed stamens are hairy and about 2 mm long and the
anthers are about 0.5 mm long. In the female flowers are obovate, 2 to 3 mm long and hairy, insulated draft tube
ovary with a short fluffy hairy
stylus, which ends in a three-part scar and eight staminodes present. The conspicuous,
membranous, almost spherical or broad pear-shaped capsule fruits have a diameter of 3 to 5 cm, initially fluffy hairy, light green "balloons" brown when ripe. There is only one seed in each of the three fruit chambers. A noticeable feature of the individual seeds is a large, light heart-shaped spot on the otherwise almost black seed. The kidney-shaped seeds have a diameter of about 6 mm and at their base a white, heart-shaped aril about 5 mm wide.
Similar species Cardiospermum grandiflorum, being very similar to
C. halicacabum, is a large growing, semi-woody perennial, whereas
C. halicacabum is smaller in size, less woody and usual an
annual plant.
C. grandiflorum also features larger fruit than the more close-packed fruit of
C. halicacabum. A kidney-shaped
hilum exists on
C. halicacabum seeds and a round hilum on
C. grandiflorum seeds. Furthermore, the leaves and stems of
C. grandiflorum have small reddish hairs that lack in
C. halicacabum. Lastly,
C. grandiflorum has larger flowers than those of
C. halicacabum. ==Medicinal uses==