Nasturtium (not native)

Most people recognize vining nasturtiums (Tropaeolum majus), the perky standards of California gardens. Few people, however, have looked closely enough to see the psychedelic display of color deep in a flower’s throat. These patterns may be signal patterns to direct pollinating insects toward the nectar source, deep in the spur behind the petals.

This same easy-care vine, has become a serious pest in California’s coastal wildlands. Nasturtiums originated in the Andes and have been introduced in gardens around the world. In some areas of the Reserve, where runoff from nearby houses provides a bit more fresh water, feral nasturtiums’ engulf trails, trail signs and even large shrubs. A prolific reseeder with few pests, a plant not only produces many offspring, but new seeds are continually entering the Reserve from adjacent gardens, making it difficult – if not impossible – to eradicate.

Description ^{4,11,59,241,306,400}

Nasturtium is a long-stemmed, sprawling annual or perennial vine that can be a ground cover or can lean on and climb up through shrubs and small trees, clinging by means of long petioles that loop around support structures. Stems are somewhat fleshy and smooth and can grow to 10 feet (3 m), persisting as shredded curtains long after they have died back. The leaves are approximately circular, often with a few broad, shallow lobes; they are attached to the petiole near the leaf center with veins radiating from the point of attachment. The largest leaves maybe five inches (13 cm) across. Nasturtiums contain mustard oils that give the entire plant a peppery taste.

The showy, funnel-shaped flowers are bisexual and bilaterally symmetrical, to 2½ inches (6 cm) across. There are five unequal sepals that are pale green to yellowish and marked with dark red veins. The two lower sepals are narrow triangles, the three upper sepals are triangular, partially fused below; the fused upper sepals extend down from the flower in a long spur that conceals the nectar glands. Outside the garden, the petals are usually orange with yellow and or red markings but may be yellow or red. Petals are unequal. The three lower petals are rounded with a long basal claw. Between the blade and the claw is a fringe of linear projections, like eyelashes, typically bright orange with orange to dark red tips. The two upper petals are obovate to wedge-shaped with dark red veins converging towards the narrowed base. There are eight stamens of unequal length, and one pistil with a superior, three-chambered ovary and a style with a three-forked stigmatic tip. The main bloom time is March – June,⁷ but isolated flowers may be found at other times.

The fruit is round to ovoid, three-lobed, consisting of three wrinkled segments with longitudinal ridges. The segments split into separate subunits on maturity. Each segment contains a single ovoid seed.

Classification ^2,11,44

Nasturtium is a dicot angiosperm in the nasturtium genus, Tropaeoleum, the only genus in the nasturtium family, Tropaeolaceae, This is a family originating in South America and characterized by twisting, slightly fleshy stems and showy, bilaterally symmetrical flowers with a nectar-producing spur and eight stamens in two ranks. The closest relatives of this family are the mustards (Brassicaceae) and capers (Caperadaceae). There is one other common nasturtium: the less hardy bush-type, Tropaeolum minus,³⁰⁶ but it is not known to have naturalized.

Plants in the Tropaeolaceae contain mustard oils similar to those in watercress and these give them a peppery taste. The common name, nasturtium, comes from the watercress genus, Nasturtium, because of the similar peppery taste. The two, however, are not closely related. (The word itself, in Latin, means “nose twist”, presumably because of the zingy pepper-taste of the plants.⁴⁵⁵)

Ecology ^458,464

Like other flowers with bilateral symmetry, such as snapdragons and sages, the shape of nasturtium is thought to be an adaptation to attract certain pollinators.⁴⁶⁵ In nasturtium, the nectar is produced and held in the tip of the long spur, accessible through the flower, mainly by pollinators with long tongues, especially hummingbirds and some bees. As an inducement, the sugar content of Tropaeolum may be the highest of any flower. Just in case bees and hummingbirds are not active, nasturtiums have a back-up strategy. If nectar is unharvested, it will accumulate and fill the spur and then becomes accessible to smaller pollinators.

The broad, flattened shape of the lower petals may act as a landing platform for bees while the bright stripes at the base of the upper petals guide the bird or insect toward the nectar-containing spur.^463,465

All of this is consistent with studies and conclusions based on other species. But I have yet to learn of a possible adaptation for the fringe, the eyelashes, that partially close the flower throat. Could they serve as a barricade to direct the pollinator toward the stripes at the other side of the throat?

Human Uses ^455,458,462

Nasturtium is best known as a cheerful, carefree garden flower. Dutch botanists introduced the vining nasturtium to Europe from Peru in the 17th century. By the early 18th century, nasturtiums were growing in the gardens of Louis XIV and by mid-to-late century, Thomas Jefferson was planting them at Monticello. In the late 19th century, Monet established rambling beds of nasturtiums at Giverny, visible in some of his paintings. All the while, horticulturists were developing new forms and new colors. Today there are spurless forms, forms with double flowers, forms that raise the flowers well above the leaves, and there are flowers in a rainbow of colors – both multi-colored forms and single color forms.

Culinary uses, only less well known, are equally varied: nasturtiums can be used in salads, stir-fries, pasta; you can stuff the flowers for appetizers or pickle the seed pods as a substitute for capers. One restaurant in the San Francisco Bay area makes their own nasturtium-flavored soda.⁴⁵⁷ A Nature Collective board member once told me he was raised on baloney and nasturtium sandwiches. I tried it with turkey – delicious.

Interesting Facts ^459,460,461

“…’Tis said, in Summer’s evening hour
Flashes the golden-colour’d flower…”
Samual Tayler Coleridge (Poems on Various Subjects, 1796)

One evening in the mid-sixteenth century, Elizabeth Linnaeus, the daughter of Swedish botanist Carl Linnaeus, was relaxing in her father’s country garden. As the light faded, Elizabeth noticed that the orange flowers of the nasturtium seemed to flash and spark. She confirmed this observation with her father and several friends and ultimately published a paper under the auspices of the Swedish Royal Academy of Sciences. Her observations were soon repeated by others and given the name “Elizabeth Linnaeus Phenomenon”. It was determined that not all flowers flash (blue flowers, for instance, do not), that the flashes occur mostly when the eye is moving from side to side and that the flashing is more easily seen by children and young adults.

Scientists originally attributed the flashing to phosphorescence, or to some electrical emanation of the plant, but in 1914, a German professor demonstrated that the flashes originate, not from the plant, but from the eye, an after-image caused by the interaction of red light, the primary wave length at twilight, and the rods and cones of the retina.

Meanwhile, the imagery of twinkling, sparking flowers caught the imagination of several writers and poets of the time and was immortalized in the Romantic age of literature by poets such as Coleridge and Wordsworth.

“… They flash upon that inward eye
Which is the bliss of solitude;
And then my heart with pleasure fills,
And dances with the daffodils.”
William Wordsworth (I Wandered Lonely as a Cloud, 1815)