Campbell Island Bittercress
Cardamine subcarnosa
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Campbell Island bittercress (Cardamine subcarnosa) is a small perennial herb in the mustard family found only on Campbell Island, New Zealand's southernmost subantarctic island group. It forms open rosettes of glossy, slightly fleshy, divided leaves up to 140 mm long and sends up flowering stems to 300 mm carrying small white, pink or purple flowers, followed by slender seed pods. It grows in damp scree, peat, grassland and rock crevices, especially in the summit herbfields and fellfields. Because it is confined to one island under 1000 square kilometres, it is ranked At Risk - Naturally Uncommon. It is not known in cultivation. Explore more native flowering plants in our native plant guide.
Plant Description
Cardamine subcarnosa is a tufted perennial herb that forms an open rosette. The leaves are pinnately divided, usually up to 100 mm and occasionally 140 mm long, green, glossy and somewhat leathery. Each leaf has 5 to 7 leaflets, mostly in pairs, with a rounded to broadly elliptic end leaflet. The leaf and stalk margins are sparsely fringed with hairs or almost hairless.
The flowering stems reach up to 300 mm and carry small four-petalled flowers typical of the mustard family. The petals are 2.2 to 4.7 mm long and may be white, pink or purple. The fruit is a narrow silique 9 to 20 mm long and about 1 mm wide, containing red-brown wingless seeds.
Its closest relative on the subantarctic islands is Cardamine latior. Campbell Island bittercress has longer leaves with fewer, non-overlapping leaflets, longer inflorescences and narrower siliques that lack a well-defined central vein in the dividing wall.
Quick Facts
| Scientific Name | Cardamine subcarnosa |
|---|---|
| Height | Flowering stems up to 0.3 m |
| Spread | Rosettes up to about 0.3 m across |
| Water Needs | Constantly damp |
| Light | Open, exposed sites |
| Frost Tolerance | High; a subantarctic species |
| Salt Tolerance | No information available |
| Growth Rate | No information available |
| Lifespan | Perennial |
Climate Best Suited to
Adapted to the cold, cloudy, wet and windy oceanic climate of Campbell Island, with cool summers and frequent rain. NZPCN expects it would struggle with heat and humidity.
Regional Suitability
| City | Climate Suitability |
|---|---|
| Auckland | Low |
| Wellington | Low |
| Christchurch | Low |
| Dunedin | Medium |
Plant Habitat
This species is endemic to Campbell Island, more than 600 km south of Stewart Island/Rakiura. Herbarium collections come from places such as the western slope of Mount Honey, Tucker Cove and the summit of Mount Azimuth, showing that it occurs from near sea level to the island's tops.
It grows in damp places on scree, peat, grassland and in rock crevices. It is most at home in herbfields, tall Marsippospermum rushland and the fellfields of the summit tundra zone, where cold, wet and windy conditions keep vegetation low.
Growing Requirements
Soil Requirements
Campbell Island soils are mostly wet peats and thin mineral soils over rock. The bittercress roots into damp peat, scree and crevices.
- Moist, peaty or gritty substrate
- Cool root run among rocks
- Never allowed to dry out
Light Requirements
It grows in open, low vegetation where it is not shaded by shrubs, under the frequently overcast subantarctic sky.
- Open sites in short herbfield and fellfield
- Shelter of rocks and crevices
Water Requirements
Rain falls on most days of the year on Campbell Island, and the species occupies consistently damp ground.
- Requires steady moisture
- Cool, moist air matters as much as soil moisture
Planting and Establishing
Cardamine subcarnosa is not known in cultivation and is not available from nurseries. Campbell Island is a nature reserve and World Heritage site, so plants or seed must not be collected without permits.
If grown for research or conservation, NZPCN's comment that it would likely suffer in high temperatures and humidity suggests a cool alpine house or a shaded, moist trough in a cool southern garden would be the best attempt.
Ecological Role
NZPCN records that the seeds are dispersed by ballistic projection, as the ripe siliques split explosively and fling seed outwards, and also by water and by attaching to passing animals. No information was found on its pollinators; small flies are the main flower visitors on the subantarctic islands generally.
Since sheep, cattle and rats were removed from Campbell Island, its herbfields have been recovering, and plants of damp open ground such as this bittercress are part of that regenerating megaherb and herbfield vegetation.
Uses & Significance
Garden Uses
It has no established garden use because it has never been cultivated.
- Potential subject for alpine house or research collections
- Interest for subantarctic flora displays
Ecological Value
As a Campbell Island endemic it contributes to the distinctive plant diversity of the New Zealand subantarctic islands.
- Endemic element of Campbell Island herbfields
- Provides flowers for small subantarctic insects
- Colonises damp scree and rock crevices
Landscaping Uses
There is no landscaping use for this species. In botanical displays it would sit well in a cool, damp rock garden or trough with other low subantarctic and alpine herbs.
Gardeners wanting a native Cardamine for a moist shady spot would do better with a mainland species suited to local conditions.
Seasonal Care Calendar
Spring
Rosettes resume growth as the short subantarctic growing season begins.
- New leaves expand from the rosette centre
Summer
Flowers appear from about November to February, followed by siliques from December to February.
- White, pink or purple flowers
- Seed pods ripen
Autumn
Pods finish shedding seed and the plant settles back to a leafy rosette.
- Seed dispersal ends
Winter
Plants persist as rosettes through the cold, wet Campbell Island winter.
- Growth largely stops
When to Prune and How Much
No pruning is needed. In cultivation, spent flowering stems could be removed after seed has been collected to keep the rosette tidy.
Remove any yellowing or rotting leaves from the rosette centre to reduce disease risk in humid weather.
How to Grow Campbell Island Bittercress
NZPCN states that Cardamine subcarnosa is not known from cultivation, so there is no proven propagation method. It describes the plant as probably easy to grow, but likely to suffer in high temperatures and humidity. The notes below are based on how related Cardamine species are normally raised and would need testing. Any seed or plant material must be obtained under permit from Campbell Island.
From Seed
Cardamine seed is small and usually germinates readily when fresh. Because the siliques open explosively, pods are best collected just as they begin to turn colour and allowed to finish ripening in a paper bag. Given the plant's cold, wet home, germination and growing on should be attempted in cool conditions, ideally in an unheated, well-ventilated alpine house or shade house rather than a warm propagating unit, and seedlings should be protected from slugs.
- Collect nearly ripe siliques in a paper bag so seed is not lost.
- Sow seed on the surface of a moist, gritty seed mix.
- Cover lightly with fine grit.
- Keep cool, moist and in bright shade.
- Prick out seedlings into small pots once they have a few leaves.
By Division
Larger tufted plants with several crowns may be split, as is done with other perennial Cardamine. This should only be tried on cultivated stock.
- Lift the plant in cool weather.
- Separate crowns with some roots attached.
- Replant into moist gritty mix and keep cool until established.
Pests & Diseases
No pests or diseases have been recorded for this species. In cultivation, plants of the mustard family are prone to aphids, white butterfly caterpillars, slugs and snails, any of which could damage a small rosette.
Heat and humidity are the likely main problem, leading to rot. A cool, airy position would be essential.
Cultural Significance
No Māori name or traditional use is recorded for Cardamine subcarnosa, which is confined to a remote subantarctic island.
It was first described by Joseph Dalton Hooker from material gathered on Campbell Island during the Antarctic Expedition of 1839 to 1843, originally as a variety of Cardamine hirsuta. Harry Allan raised it to species rank in his Flora of New Zealand in 1961.
Bonus Tip
If you visit Campbell Island on an approved expedition, look for this bittercress in damp rock crevices and summit fellfield rather than in the tall megaherb meadows. Its glossy, slightly fleshy divided leaves and narrow upright seed pods are the giveaway, and photographs uploaded to iNaturalist help build a picture of its distribution.
Related Plants
Explore other native plants that share similar characteristics or habitats with Campbell Island Bittercress (Cardamine subcarnosa), offering further insights into New Zealand's diverse flora. These related species provide context and opportunities for complementary planting in your garden.
Plant Conservation
Cardamine subcarnosa is ranked At Risk - Naturally Uncommon (2023) because its entire range is on one island of less than 1000 square kilometres. Qualifiers note it is data poor for size and trend, an island endemic, and found at a single location.
Campbell Island is protected as a nature reserve and part of the New Zealand Subantarctic Islands World Heritage Area. The eradication of sheep, cattle and Norway rats has greatly reduced pressure on its herbs, and strict biosecurity to keep new pests and weeds out is the most important ongoing protection.
Frequently Asked Questions
What is Campbell Island bittercress?
It is Cardamine subcarnosa, a rosette-forming perennial herb in the mustard family Brassicaceae that grows naturally only on subantarctic Campbell Island.
Why is it called subcarnosa?
The epithet comes from Latin sub, a little, and carnosa, fleshy, and probably refers to its somewhat fleshy, glossy, leathery leaves.
How do you tell Cardamine subcarnosa from Cardamine latior?
NZPCN notes that Cardamine subcarnosa has longer leaves with fewer leaflets that do not overlap, longer flowering stems, and narrower seed pods without a well-defined central vein in the septum.
Can you grow Campbell Island bittercress?
It is not known from cultivation. NZPCN suggests it would probably be easy to grow but would likely suffer in high temperatures and humidity.
Sources and Further Reading
The botanical, growing, and conservation details for Campbell Island Bittercress (Cardamine subcarnosa) on this page draw on the New Zealand plant references below. Consult them for full technical records and the latest distribution data.