Neotropical Balsaminaceae

Description

Herbaceous, semi-succulent, erect, glabrous plants, never woody. Leaves generally petiolate, with two distal glands, venation pinnate, margin entire to variously crenate or dentate, leaf-blades fleshy when alive, drying membranaceous; stipules absent. Inflorescences of axillary small cymes or fascicles, or flowers solitary. Flowers hermaphrodite, with bilateral symmetry, hypogynous, calyx (3-)5-merous, lobes fused and forming a nectar-secreting spur, corolla 5-merous, lobes fused, showy, brightly coloured, white, pink, salmon, red or mauve; stamens 5, minute, filaments and anthers connate into a calyptra above gynoecium, anthers dehiscing longitudinally; ovary superior, 5-locular, with many ovules with axillary placentation. Fruit a fleshy capsule, opening by explosive longitudinal dehiscence with valves curling up, 10-20-seeded; seeds generally rounded, testa smooth, matt, brown, embryo straight, endosperm lacking or little.

Notes on delimitation

• Placed within the Ericales, together with Marcgraviaceae (APG II, 2003).

Distribution in the Neotropics

• Introduced into the Neotropics, represented by a single species, Impatiens walleriana Hook. f., very widespread in the Atlantic Forest of Brazil and known as 'Maria Sem Vergonha'. Other species cultivated as ornamentals.

Distinguishing characters (always present)

• Filaments and anthers fused over gynoecium forming a calyptra.
• Capsule explosively dehiscent with valves curling up.

Other important characters

• Plants herbaceous.
• Semi-succulent.
• Stem translucent.
• Flowers showy with bilateral symmetry.

Key differences from similar families

• Differs from Begoniaceae by hermaphrodite flowers and symmetric leaves.
• From many other herbaceous plants by the particular arrangement of its stamens over the gynoecium, which apparently avoids self-pollination.

Number of genera

• 1: Impatiens L.

Notable genera and distinguishing features

n.a.

Status

• A few species cultivated in gardens, I. walleriana naturalized in Eastern Brazil.

Important literature

APG II, 2003. An update of the Angiosperm Phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4): 399-436.