Swamp Pennywort

Botanical name: Hydrocotyle novae-zeelandiae var. novae-zeelandiae
Synonyms: None
Common name(s): Swamp pennywort

About:
A small, creeping perennial herb endemic to New Zealand, Hydrocotyle novae-zeelandiae var. novae-zeelandiae forms extensive patches of rounded, shallowly divided leaves on creeping stems.

The species is quite variable in appearance. Leaves may be dull green, greenish-brown or bright glossy green and range from completely hairless to densely hairy. They are divided into 5–7 relatively broad segments, giving the foliage a softly scalloped or toothed outline.

Despite its common name, swamp pennywort is not restricted to wetlands. It is a facultative wetland plant and may occur in both wet and comparatively well-drained habitats.

Natural habitat:
Occurs in moist and damp habitats including wetlands, swamp margins, stream and seepage margins, damp grassland, forest clearings and other low-growing vegetation.

It is capable of occupying both wetland and non-wetland sites where sufficient moisture and open ground are available.

Growing environment:
Frost, Sun, Partial Shade, Wet Soil & Moist Soil tolerant. Best in consistently moist ground but adaptable to a range of conditions.

Endemic distribution:
Endemic to New Zealand.

Hydrocotyle novae-zeelandiae is represented by several geographically and morphologically differentiated varieties within New Zealand.

Height:
Approximately 2–10 cm tall.

Width:
Spreading indefinitely by creeping stems and capable of forming extensive patches.

Flowering:
October – December

Produces small, inconspicuous flowers in simple umbels containing approximately 5 to many flowers.

Fruiting:
November – March

Produces relatively broad, hairless fruits approximately 1.8–3.5 mm long by 1.8–2.5 mm wide.

Uses:
• Native groundcover
• Wetland planting
• Swamp and seep margins
• Streamside planting
• Damp woodland gardens
• Underplanting
• Naturalistic native gardens
• Low-growing restoration planting
• Ground cover around sedges and rushes

Appearance:
Growth habit:
A perennial creeping herb forming broad, low-growing patches.

Stems vary from relatively slender to stout and spread horizontally through surrounding vegetation and across suitable ground.

Leaves:
Leaves are simple and approximately 5–35 mm in diameter.

Colour is variable, ranging from dull green and greenish-brown through to bright glossy green.

Hairiness is also highly variable, with some plants almost completely glabrous and others densely hairy on both leaf surfaces.

Leaves are divided approximately one-fifth to one-third of the way toward the centre into 5–7 segments.

The individual segments range from triangular to broadly oblong-obovate and may themselves be obscurely three-lobed.

Margins are crenate or serrate and occasionally terminate in short hair tips, but remain essentially flat rather than strongly curled or folded.

The petiole may have only a few backward-pointing hairs near the blade or be densely hairy throughout.

Flowers:
Flowers are minute and visually inconspicuous.

They are arranged in simple umbels containing five to numerous flowers.

Flowering stalks are generally shorter than or approximately equal in height to the leaves, keeping the flowers close to the surrounding foliage.

Individual flowers are virtually stalkless or borne on short pedicels.

Fruit:
Fruit is hairless and comparatively large for a small Hydrocotyle, approximately 1.8–3.5 × 1.8–2.5 mm.

The dorsal edge is usually rounded.

The ribs are normally slightly impressed or engraved into the surface of the mature fruit rather than prominently raised, although occasionally they may be slightly elevated.

At maturity the fruit separates into mericarps, which are dispersed by wind and water.

Ecology:
Hydrocotyle novae-zeelandiae var. novae-zeelandiae contributes to the low ground layer of wetland margins and other moist native plant communities.

Its creeping stems allow established plants to spread across exposed soil and between larger wetland herbs, sedges and rushes.

Although associated strongly with damp habitats, its facultative wetland status reflects its ability to grow both as a hydrophyte in wet environments and as a terrestrial herb in suitable non-wetland situations.

The mericarps are dispersed by water and wind. Water dispersal is particularly useful in wetland environments, where seeds may be transported between suitable patches of habitat.

Associated habitats:
Wetlands, swamp margins, seepages, stream margins, damp grassland, moist open ground, forest clearings, wet depressions and low-growing native vegetation.

How to grow:
Plant into consistently moist soil in full sun or partial shade.

It is particularly well suited to the margins of ponds, wetlands, swales and other areas where the ground remains damp without necessarily being permanently submerged.

For a dense groundcover, plant several rooted pieces across the desired area and maintain reliable moisture during establishment.

Once established, the creeping stems spread naturally into surrounding open ground.

It can also be grown amongst native sedges, rushes and other moisture-loving groundcovers to reproduce the layered appearance of natural wetland vegetation.

Propagation:
Very easily propagated by division of established patches.

Lift sections containing rooted creeping stems and foliage, divide into smaller pieces and replant directly into moist soil.

Keep newly planted divisions consistently moist until active new growth confirms establishment.

Propagation from seed is also possible. Mature fruits may be collected during the November–March fruiting period and sown into a consistently moist propagation medium.

Cultural use:
No specific traditional Māori use is widely documented for Hydrocotyle novae-zeelandiae var. novae-zeelandiae.

The botanical name novae-zeelandiae means “of New Zealand”, reflecting the species’ New Zealand origin.

Garden value:
A useful endemic groundcover for damp native gardens, wetland margins and naturalistic plantings.

Its variable green foliage forms a soft, low carpet beneath taller wetland plants and provides a useful transition between open water or saturated ground and larger sedges, rushes, ferns and shrubs.

Its small size also makes it valuable for detailed ecological plantings where retaining a diverse native ground layer is important rather than relying entirely on larger, more conspicuous species.