Cranwell’s Iris

Botanical name: Libertia cranwelliae
Synonyms: None
Common name(s): Cranwell’s iris, Cranwell’s mikoikoi, native iris, New Zealand iris

About
Libertia cranwelliae is an exceptionally rare endemic New Zealand iris restricted to the East Cape of the North Island. It is a distinctive spreading perennial that produces fans of long, narrow leaves from bright yellow horizontal stolons. Unlike the more clump-forming appearance typical of many Libertia, its far-creeping stolons allow new leafy fans to emerge some distance from the parent plant. White iris-like flowers appear during spring, followed by unusually large barrel-shaped capsules that change from green through yellow-orange to black or grey-black. The species is currently classified Threatened – Nationally Critical, making it one of New Zealand’s most threatened native Libertia.

Natural habitat
Naturally associated with coastal forest around the East Cape, where it grows on cliff faces, seepages and stream and river banks. These environments provide relatively sheltered conditions with reliable moisture while still allowing sufficient drainage and light.

The species was historically known from several East Cape localities but has disappeared from some former sites. Its remaining natural habitat is vulnerable to browsing animals, invasive plants and habitat disturbance.

Growing environment
Best grown in partial shade to filtered sunlight in moist, humus-rich but reasonably well-drained soil. Its natural occurrence beside streams, seepages and within coastal forest indicates a preference for reliable moisture, particularly during active growth.

Although it tolerates brighter conditions, foliage exposed to strong full sun can turn yellow. A sheltered position replicating an open forest margin or stream bank is therefore preferable to a hot, exposed site.

Endemic distribution
Endemic to New Zealand and naturally restricted to a very small area of the East Cape, North Island, from near Hicks Bay south toward the Kōpuapounamu Valley.

The species was rediscovered in the wild in 2006 after having become extremely scarce, with approximately 30 plants reported from a coastal forest site near East Cape at that time. It has not been rediscovered at some of its former localities, including the Awatere River and Kōpuapounamu Valley.

Height
Leaves approximately 150–900 mm long. The flowering stems are shorter than the leaves, so the flowers and fruit are generally held within the foliage rather than extending above it.

Width
Potentially considerably wider than its height because of its long horizontal stolons. Individual leafy fans may emerge at intervals some distance from the original plant, allowing established colonies to spread progressively across suitable ground.

Flowering
September–November. Flowers are approximately 20–35 mm across and predominantly white, occasionally developing from yellowish or brown-tinged buds. Flowers are carried in narrow, sparsely branched inflorescences with

approximately 1–3 flowers on each branch.

Fruiting
Capsules may persist or mature at various times throughout the year. They are large, barrel-shaped and up to approximately 20 mm long, changing from green through yellow-orange before eventually becoming black or grey-black. Seeds are released as the largely indehiscent capsule eventually deteriorates or splits slightly.

Uses

• Conservation collections

• Ex-situ preservation

• Specialist native gardens

• Shaded or semi-shaded borders

• Streamside-style planting

• Moist woodland gardens

• Containers and conservation displays

• Educational collections of threatened New Zealand flora

• Groundcover where its spreading habit can be accommodated

Because of its Threatened – Nationally Critical status, conservation and maintenance of genetically documented cultivated material are particularly important.

Appearance
Growth habit: A perennial monocot producing numerous upright leafy fans from far-spreading horizontal stolons. Fans may be crowded together or emerge at intervals along the stolons. The stolons are approximately 3–5 mm in diameter and characteristically bright yellow, providing one of the most useful features for distinguishing this species from related Libertia.

Leaves: Long, narrow and sword-like, approximately 150–900 × 5–11 mm. Both leaf surfaces are similar in appearance, with numerous veins and the central veins crowded together to form a midrib. Leaf margins are smooth rather than rough. The leaf bases are yellow, while foliage is normally green but has a tendency to become yellowish when exposed to strong sunlight.

Flowers: White and approximately 20–35 mm diameter, with the tepals spreading widely. The outer tepals are elliptical, relatively narrow and usually more than half as long as the inner tepals. Inner tepals are broader, oval-elliptical and characteristically cleft at their tips. Anthers are approximately 3 mm long and yellow. Flowers are produced on stout, hairless pedicels approximately 5–16 mm long.

Fruit: Large, ribbed, barrel-shaped capsules reaching approximately 20 mm long. Capsules mature through a distinctive sequence from green to yellow-orange and eventually black or grey-black. They generally remain largely closed, although the apex can split slightly. Seeds are released as the mature capsule breaks down.

Ecology
A highly localised component of East Cape coastal forest, cliff, seepage and riparian vegetation. Its long stolons provide an effective means of vegetative spread, allowing established plants to form colonies by producing new leafy fans away from the original crown.

The seeds are small, approximately 1.5 × 1.5 mm, globose to angular and orange-brown. Seed dispersal is thought to include wind movement after the mature capsule disintegrates.

The remaining wild populations are particularly vulnerable because of their extremely restricted distribution. Browsing and trampling by goats, cattle and red deer, competition from invasive plants and degradation of coastal forest habitat are significant threats.

Associated habitats
Occurs within coastal forest and associated cliff, seepage, stream-bank and river-bank vegetation of the East Cape. It favours relatively moist situations within these environments rather than dry, exposed grassland or alpine habitats.

Its combination of creeping stolons and moisture preference allows it to occupy banks, forest openings and other relatively open microsites where sufficient light reaches the ground.

How to grow
Despite its extreme rarity in the wild, Libertia cranwelliae is considered straightforward to cultivate. Grow in partial shade or filtered sunlight in fertile, moisture-retentive soil with reasonable drainage. Avoid excessively hot, dry positions and prolonged drought.

Plants can tolerate some direct sunlight, but strong exposure may cause the foliage to become yellow. A position receiving morning sun or broken woodland light is likely to produce more naturally green foliage.

Allow sufficient room for the stolons to spread. New fans can emerge some distance from the original plant, so it should not necessarily be treated as a tightly clumping Libertia. Plants grown for conservation purposes should retain accurate provenance information and be kept separate from other Libertia where maintaining genetic integrity is important.

Propagation
Very easily propagated by division. Established plants naturally produce separate leafy fans along their spreading stolons, and sections containing healthy foliage, stolon and roots can be separated and replanted.

Fresh seed also germinates readily. Collect mature capsules and sow the orange-brown seed into a moist, free-draining propagation medium. Seed propagation is particularly valuable for conservation collections because it preserves greater genetic diversity than repeated vegetative division of individual clones.

Given the species’ Nationally Critical conservation status, cultivated plants of known wild provenance can have significant conservation value and should be carefully documented.

Cultural use
The common name mikoikoi is associated with New Zealand native Libertia. However, specific traditional Māori uses attributable exclusively to Libertia cranwelliae are not well documented, and uses recorded for other mikoikoi should not automatically be assigned to this species.

Its natural distribution lies within the East Cape, an area of strong cultural significance to local iwi, making protection of the remaining wild populations and their habitats particularly important.

Garden value
An attractive and botanically significant native iris combining long sword-like foliage, delicate white spring flowers, colourful developing seed capsules and an unusual spreading growth habit. Its bright yellow stolons and widely separated leafy fans distinguish it from more familiar native Libertia.

For ordinary gardens it works well in moist woodland-style plantings, partially shaded borders and alongside streams or water features where the soil remains reliably moist without becoming permanently stagnant.

Its greatest value, however, is conservation. With Libertia cranwelliae currently classified Threatened – Nationally Critical and surviving naturally within an extremely restricted East Cape range, responsibly maintained cultivated populations can provide an important safeguard for this exceptionally rare component of New Zealand’s flora.