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Tropaeolaceae


This small family is native to Central and South America. One species (Tropaeolum majus), frequently cultivated in gardens as "Nasturtium", is occasionally naturalised to become a minor weed of moist, disturbed sites in southern Australia.

Characteristic features of the family Tropaeolaceae in Australia include:

  • scrambling or climbing herbs with soft, fleshy stems and water-repellent, orbicular leaves with the petiole joined in the centre (peltate), smelling of mustard when crushed
  • flowers large, solitary, zygomorphic, yellow, orange or red, with a 2-lipped, spurred calyx and 5 clawed petals
  • ovary superior, developing into a warty or rugose, rather fleshy fruit that splits into 2 or 3 articles

Description

Annual herbaceous scrambling vines, or terrestrial herbs. Stem internodes hollow. Internal secretions not obvious, or of essential oils. Plants glabrous. Leaves alternate and spiral, cauline, petiolate, peltate. Stipules absent. Lamina simple, symmetric, orbicular; margins entire, ±flat; palmately veined, with the midrib inconspicuous and the tertiary venation reticulate; surfaces not punctate; herbaceous or succulent; distinctive odour absent or aromatic. All the flowers bisexual. Inflorescences axillary, consisting of solitary flowers. Bracts and bracteoles absent. Pollination by insects. Flowers fragrant, stalked. Floral disc absent; nectaries ?absent or present on perianth. Free hypanthium ±present. Perianth irregular, of 2 dissimilar whorls, imbricate in bud. Calyx segments fused, with 5 lobes; calyx cup-shaped or funnel-shaped, herbaceous; base with spurs or pouches. Corolla segments free, with 5 petals, alternating with the calyx lobes; corolla 1- or 2-lipped or with palate, white, yellow, orange or red, without contrasting markings, or streaked, spotted, etc, membranous; claws present; lobes ±entire or emarginate, bifid or bilobed. Fertile stamens 8, not clearly correlated with the calyx lobes, free of the corolla, free of the ovary and style, distinct from each other, all ±equal. Staminodes present or absent. Anthers basifixed, not versatile, opening sideways by longitudinal slits, 2-celled. Ovary superior and sessile. Carpels 3 (4), fused; ovary with 3 (4) locules. Style terminal, single and branched above. Ovules 1 per locule, sessile; placentation apical. Fruit dry or fleshy, a schizocarp forming fleshy, drupe-like mericarps (baccarium). Disseminule macro-surface winged or costate; micro-surface rugose, cream or brown, conspicuously patterned, dull. Seed 1 per fruit. Aril absent. Cotyledons 2. Embryo straight.
(Note: this description has been generated from the coded data compiled for the key. Any errors in the key data will be reflected in the descriptions.)

A treatment of the family Tropaeolaceae has not yet been published in the Flora of Australia. It will appear in Volume 27.

Australian genera of Tropaeolaceae (as recognised for the Flora of Australia)

* = all species introduced

*Tropaeolum


Tropaeolum majus (flowers)
Photo: K.Thiele ABRS