Pōwhiwhi

Botanical name: Ipomoea cairica
Synonyms: None commonly used in New Zealand
Common name(s): Pōwhiwhi, Coastal Morning Glory, Railway Creeper, Railroad Creeper

About:
A vigorous, perennial climbing and scrambling vine with distinctive deeply divided, hand-shaped leaves and large funnel-shaped pink-purple to violet flowers. Ipomoea cairica spreads through both climbing stems and persistent underground rhizomes, allowing established plants to form extensive colonies over coastal vegetation, dunes, banks and rocky ground.

It is indigenous to New Zealand but not endemic, occurring naturally across a wide tropical and subtropical range overseas. Within New Zealand its genuinely indigenous distribution is primarily northern and coastal, although cultivated plants have escaped and naturalised well beyond the probable original range.

Natural habitat:
Primarily coastal.

Occurs naturally in coastal dune systems, coastal scrub, cliff-face vegetation, rocky and rubble slopes and around mangrove communities.

It can scramble across open ground or climb through shrubs and other vegetation. Naturalised populations also occur around disturbed urban sites, waste ground, rubbish dumps, hedges, roadsides and other modified habitats.

Growing environment:
Sun, Coastal Exposure, Salt, Wind, Drought & Free draining tolerant. Prefers warm, sunny conditions and is particularly well adapted to sandy and disturbed coastal soils.

Frost sensitive, although established plants may survive light frost by dying back above ground and resprouting from their underground rootstock when warmer conditions return.

Endemic distribution:
Indigenous but not endemic to New Zealand.

Naturally recorded from the Kermadec Islands, including Raoul, Macauley and Cheeseman Islands, Manawatāwhi / Three Kings Islands, northern North Island and Aotea / Great Barrier Island.

Its original southern limit in the North Island is uncertain because it has been widely cultivated and subsequently naturalised. The Waitematā Harbour area is considered a likely natural southern limit, although Tiritiri Matangi Island has also traditionally been cited.

Outside New Zealand it has a very broad distribution through tropical and subtropical parts of Africa, Asia, Australia, Central America and numerous Pacific islands.

Height:
A climbing or scrambling vine rather than an upright plant.

Stems can climb several metres through surrounding vegetation and may exceed 10 m under favourable conditions.

Width:
Potentially several metres or more.

Its creeping rhizomes and vigorous stems can produce extensive colonies where growth is unrestricted.

Flowering:
September–July, with flowering often strongest during the warmer spring and summer months.

Fruiting:
September–August.

Dry capsules mature following flowering and contain hairy seeds.

Uses:
• Coastal revegetation within its natural range
• Sand binding and dune stabilisation
• Coastal erosion control
• Native coastal habitat restoration
• Rapid vegetation cover
• Wildlife and invertebrate habitat

Its vigorous growth means it should be used cautiously in gardens and restoration projects.

Appearance:
Growth habit:
A perennial rhizomatous vine with long, scrambling or climbing stems.

Young stems are relatively smooth and often reddish-green to purple. Older stems become greyish and develop a conspicuously rough or tuberculate surface.

The stems may climb through shrubs and other vegetation or spread horizontally across open ground.

Leaves:
Leaves are particularly distinctive and make the species relatively easy to recognise.

The blades are approximately 3–10 cm long and palmately divided almost to the base into usually 5–7 lobes, creating a hand-like appearance.

Individual lobes are lanceolate, elliptic or occasionally obovate, with pointed to blunt tips. The outer lobes may themselves be unequally divided.

Leaves are borne on slender petioles approximately 2–6 cm long.

Flowers:
Large, conspicuous, funnel-shaped morning-glory flowers are produced singly or in small axillary clusters.

Flowers are usually mauve, violet, purple or reddish-purple, often with a deeper-coloured throat, and occasionally white.

The corolla is generally approximately 4.5–6 cm long and may reach around 5–8 cm across.

Flowers contain five stamens and are bisexual.

Fruit:
The fruit is a dry, approximately spherical capsule around 10–12 mm across.

Capsules contain several subglobose to ovoid seeds. Young seeds are densely covered with short hairs, although they may become less hairy as they mature.

Seeds may be dispersed by both wind and water.

Ecology:
Ipomoea cairica is a vigorous colonising vine particularly well adapted to warm coastal environments.

Its extensive rhizomatous root system enables it to bind loose substrates such as coastal sand and rapidly recolonise disturbed ground. Stems can scramble over open surfaces or use surrounding shrubs and other vegetation for support.

The species’ ability to regenerate from rooted pieces contributes greatly to its persistence. Broken or discarded plant material can potentially establish new colonies.

Although indigenous populations form a natural component of northern New Zealand’s coastal flora, the species can become aggressive outside its natural ecological setting. Distinguishing genuinely indigenous populations from naturalised garden escapes can therefore be difficult.

Associated habitats:
Coastal dunes, sand flats, coastal scrub, cliff faces, rocky slopes, rubble slopes, mangrove margins, coastal shrubland, disturbed ground and northern coastal forest margins.

Within modified environments it may also occur in hedges, waste ground, roadsides, urban margins and abandoned sites.

How to grow:
Extremely easy to establish but should be planted with caution because of its vigorous spreading habit.

Best suited to warm, sunny, frost-free coastal sites with freely draining soil. It performs particularly well in sandy soils and tolerates exposure, wind and salt-laden coastal conditions.

Once established it requires little attention and can spread rapidly through both stems and underground rhizomes.

Avoid planting close to sensitive native vegetation where uncontrolled growth could smother smaller plants. Its cultivation is most appropriate where its spread can be contained or in ecological restoration within its genuine natural range.

Propagation:
Very easily propagated from fresh seed, stem cuttings and rooted sections of rhizome.

Cuttings and broken rooted stems establish readily under warm conditions.

Fresh seed can also be sown into a freely draining propagation medium and maintained in warm conditions until established.

Because even pieces of established plants can regenerate, discarded material should be managed carefully to prevent unwanted spread.

Cultural use:
Known in te reo Māori as pōwhiwhi.

Specific traditional Māori uses for Ipomoea cairica are not well documented, and it should not be confused with kūmara (Ipomoea batatas), another member of the same genus with major cultural and food significance.

Garden value:
A striking native coastal vine with attractive hand-shaped foliage and large purple-pink morning-glory flowers.

Its rapid growth, long flowering period and ability to tolerate exposed coastal conditions can make it valuable for difficult seaside sites and sand stabilisation. However, those same characteristics can make it excessively vigorous in conventional gardens.

It is therefore best suited to controlled coastal plantings and restoration within its natural northern range rather than small gardens, where its rhizomes and climbing stems can become difficult to contain.