Limestone Button Daisy

Botanical name: Leptinella calcarea
Synonyms: Cotula calcarea
Common name(s): Limestone button daisy

About:
Leptinella calcarea is a distinctive endemic New Zealand button daisy restricted to a narrow strip of coastal north-west Nelson. It is a small, mat-forming perennial specially adapted to open calcareous ground, including limestone, calcareous mudstone, conglomerate rock and consolidated coastal sand dunes.

The species forms loose to compact patches of stiff, yellow-green to grey-green, deeply divided leaves that are usually covered in conspicuous long woolly hairs. Most of the plant’s wiry rhizome system remains buried, with short leafy shoots emerging at intervals above the surface.

Male and female flowers are produced on separate plants. This can make seed production uncommon in cultivation when only one sex is present.

Although naturally range-restricted and occurring in relatively small populations, it can be locally common within suitable habitat.

Natural habitat:
Coastal turf and sparsely vegetated open ground on limestone, calcareous mudstone, conglomerate rock and consolidated sand dunes.

It favours sites with minimal taller vegetation and little competition, often forming low turf across exposed mineral substrates.

Its natural habitats are strongly associated with the calcareous geology of the north-west Nelson coast.

Growing environment:
Full Sun, Coastal Exposure, Wind, Calcareous Soil, Free-draining Soil & Exposed Conditions tolerant.

It performs best in open situations where competition from taller vegetation is low.

Despite the fleshy texture of its leaves, the species naturally occupies freely draining substrates and is well adapted to exposed coastal conditions.

Endemic distribution:
Endemic to New Zealand.

Restricted to the north-western South Island in north-west Nelson, from Cape Farewell south to Kahurangi Point.

Its naturally narrow geographic range is closely associated with suitable coastal calcareous substrates.

Height:
Foliage generally approximately 1–4 cm tall, with flowering peduncles reaching approximately 1–4 cm.

Width:
Individual plants spread through underground rhizomes to form loose or compact mats, potentially reaching 20–50 cm or more across with time.

Flowering:
August–November.

Male and female flower heads occur on separate plants.

Female capitula are approximately 3–5 mm across when flowering and may expand to around 10 mm as the fruits develop.

Male capitula are approximately 4–6 mm across.

The individual florets are inconspicuous and predominantly yellow-green.

Fruiting:
September–January.

Mature cypselae are approximately 1.6 mm long and 0.8 mm wide, slightly compressed and brown.

The lightweight fruits are dispersed principally by wind and possibly by attachment.

Uses:
• Native rock gardens
• Limestone gardens
• Coastal gardens
• Native groundcover
• Crevice planting
• Specialist botanical collections
• Conservation collections
• North-west Nelson restoration
• Coastal turf restoration
• Naturalistic native planting

Appearance:
Growth habit:
A low, perennial, tufted herb forming loose to compact mats.

Most vegetative growth originates from buried rhizomes. Short shoots grow upward from these rhizomes and terminate in small clusters of approximately 3–8 leaves.

The resulting growth is low, dense and turf-like.

Male and female reproductive structures are borne on separate plants.

Rhizomes/Stems:
Rhizomes are usually well buried beneath the surface.

They are pale, slender, wiry and hairless, with relatively little branching.

Short shoots emerge from the rhizomes at intervals of approximately 5–20 mm and carry clusters of leaves at their tips.

Roots are slender and relatively weak, reaching approximately 0.5 mm in diameter.

Flowering peduncles arise from the short shoots and are approximately 10–40 mm long, generally about equal to the leaves. They are covered in long hairs and are either without bracts or carry a single small bract.

Leaves:
Leaves are approximately 10–40 mm long and 3–6 mm wide.

They are oblong to elliptic, thick, somewhat fleshy and unusually stiff and rigid.

Colour is predominantly yellow-green, occasionally grey-green.

The surfaces usually carry a moderate to dense covering of long, woolly hairs.

A prominent raised midrib is visible along the upper surface.

Each leaf is deeply divided into approximately 12–20 pairs of broad, closely spaced pinnae that usually overlap one another.

The pinnae themselves bear closely spaced, narrow triangular teeth with blunt tips.

The combination of stiff fleshy foliage, dense woolly hairs and closely overlapping pinnae is particularly characteristic of the species.

Flowers:
Flowers are grouped into small button-like capitula.

Female flower heads are initially approximately 3–5 mm across, with a convex surface and urn-shaped involucre.

They contain approximately 25–120 curved yellow-green florets, each around 2 mm long.

There are approximately 20–40 involucral bracts arranged in three or more unequal rows. These are broadly elliptic, green and hairy with broad papery margins tipped brown.

The inner bracts continue growing after flowering, temporarily enclosing the developing fruits. At maturity they bend partly outward to expose the ripe cypselae.

Male heads are approximately 4–6 mm across and hemispherical, with 8–15 involucral bracts arranged in one or two rows and numerous male florets.

Fruit:
The fruit is a small dry cypsela measuring up to approximately 1.6 × 0.8 mm.

It is slightly compressed and initially covered by a pale, unwrinkled papery membrane.

As it matures, the surface becomes smooth and brown.

Seeds:
Each cypsela contains a single seed.

The small, lightweight fruits are adapted primarily for wind dispersal, although attachment to animals or other moving material may also contribute to dispersal.

Because the species is dioecious, both male and female plants need to occur sufficiently close together for viable seed production.

Ecology:
Leptinella calcarea is a highly localised specialist of open calcareous coastal habitats.

Its deeply buried rhizomes protect much of the plant beneath the substrate, while small leafy shoots emerge into the exposed surface environment.

Its low stature helps it tolerate strong coastal winds, and its thick, rigid foliage is well suited to exposed conditions.

The species performs best where vegetation cover remains sparse. Encroachment by taller or more vigorous plants can reduce the open habitat on which it depends.

Its restricted geographic range makes it naturally vulnerable to changes in land management, habitat modification and the loss of suitable open calcareous ground.

Although individual populations can be locally abundant, many occupy relatively small areas.

Associated habitats:
Coastal limestone outcrops, calcareous mudstone, conglomerate rock, consolidated sand dunes, open coastal turf, rocky ground, exposed coastal slopes and sparsely vegetated mineral substrates.

Associated vegetation is generally low and open, including native coastal herbs, small grasses, sedges and other turf-forming species adapted to exposed calcareous environments.

How to grow:
Leptinella calcarea is one of the more horticulturally useful specialist Leptinella species.

Grow in full sun in a fertile but exceptionally free-draining soil.

A gritty mineral-rich substrate containing limestone chips or other calcareous material is particularly appropriate.

Avoid dense shade and competition from vigorous neighbouring plants, which can overwhelm its low-growing foliage.

It is particularly effective between rocks, along the edges of paths, in raised rock gardens and within limestone-themed native plantings.

Although tolerant of coastal exposure, newly established plants should be kept adequately moist until their rhizome and root systems have developed.

Propagation:
Easily propagated by division of established cultivated plants.

Small rooted sections of mat can be separated and replanted into free-draining substrate, taking care to retain healthy rhizomes and roots.

Fresh seed is also likely to germinate readily when available.

Seed is often scarce in cultivation because plants are dioecious and many cultivated collections consist of only one sex. Both male and female plants are required for successful sexual reproduction.

Wild plants should not be removed for propagation.

Cultural use:
No specific traditional Māori material use is well documented for Leptinella calcarea.

Its significance lies particularly in its status as a highly localised component of the distinctive limestone and coastal flora of north-west Nelson.

Garden value:
An excellent native rock-garden and specialist groundcover plant.

Its compact mats of finely divided, woolly yellow-green foliage provide attractive year-round texture, while the tiny yellow-green flower heads add subtle seasonal interest.

It is especially suitable for limestone gardens, rockeries, raised beds, crevices and exposed coastal plantings where larger plants would be inappropriate.

Its extremely restricted natural distribution also gives it considerable conservation and educational value, particularly within gardens showcasing the distinctive native flora of Nelson and north-western South Island.