Blue Mountain Bidibid

Botanical name: Acaena inermis
Synonyms: None
Common name(s): Blue Mountain Bidibid, Spineless Bidibid

About:
Blue Mountain Bidibid is a beautiful low-growing native groundcover valued for its soft blue-grey to purple-toned foliage and almost spineless seed heads. Unlike many other bidibid species, it lacks the strongly hooked burrs that readily cling to clothing and animals, making it a far more practical choice for gardens and areas beside paths.

Its attractive foliage, compact habit and excellent drought tolerance make it one of New Zealand’s finest native groundcovers for alpine, rock and dry gardens.

Natural habitat:
Occurs naturally in montane to alpine grasslands, riverbeds, gravel terraces and other open, well-drained habitats.

It is commonly found in exposed environments where it grows among tussocks, herbs and low alpine vegetation.

Growing environment:
Thrives in full sun and free-draining soil. It is highly tolerant of frost, drought, wind and exposed conditions once established.

The species performs best in gravelly, sandy or stony soils and dislikes prolonged waterlogging or heavy clay soils.

Endemic distribution:
Endemic to New Zealand. It occurs in the central North Island and throughout much of the eastern South Island.

Height:
Approximately 4 cm

Width:
Typically spreads 50 cm or more, gradually forming attractive mats

Flowering:
November–January, occasionally extending into March

Fruiting:
November–May

Uses:
• Native groundcover
• Rock gardens
• Alpine gardens
• Pathway edging
• Erosion control
• Bee food
• Dry garden planting
• Low-maintenance landscaping

Appearance:
Growth habit:
A creeping, rhizomatous perennial that spreads by rooting stems to form loose, low-growing mats.

Its compact habit allows it to gently cover exposed ground without becoming invasive.

Stems:
Slender creeping stems spread across the soil surface and root at the nodes, steadily increasing the size of the colony.

Leaves:
Leaves are finely divided into 11–15 rounded leaflets, creating a delicate, fern-like appearance.

The foliage varies from dull green and blue-grey to attractive purple and bronze tones, particularly during colder weather or in exposed alpine conditions.

Flowers:
Small white flowers are produced in rounded, globe-shaped heads held just above the foliage during late spring and summer.

Although individually tiny, the flower heads create an attractive display across established plants.

Fruit:
The seed heads mature to pale cream or light brown and are notable for lacking the strongly hooked barbs typical of most other bidibid species.

Any remaining spines are soft, greatly reduced or completely without barbs, making the fruit far less likely to attach to clothing or animal fur.

Seeds:
The small fruits contain individual seeds that are dispersed naturally, but without the aggressive attachment mechanism seen in many related species.

Ecology:
Blue Mountain Bidibid is well adapted to exposed alpine and montane environments where it helps stabilise loose soils and gravel.

Its spreading mats reduce erosion, suppress competing weeds and provide habitat for small invertebrates. The flowers attract a range of native pollinating insects.

The reduced or absent barbs on the fruit distinguish it ecologically from most other Acaena species, which rely heavily on attachment to animals for dispersal.

Associated habitats:
Montane and alpine grasslands, riverbeds, gravel terraces, rocky slopes, herbfields and open tussock country.

Associated plants commonly include snow tussocks, Celmisia, Raoulia, alpine Coprosma, native grasses and other drought-tolerant alpine herbs.

How to grow:
Plant in full sun in very free-draining soil. It is ideal for rockeries, gravel gardens, retaining walls and dry banks.

Water regularly while establishing, but once rooted the plant requires very little supplementary watering. Avoid heavy soils that remain wet through winter.

Allow plants room to spread naturally or trim lightly to maintain tidy edges where required.

Propagation:
Propagation is easy by division of established plants or rooted stem sections.

Fresh seed may also be sown into a free-draining seed-raising mix and kept lightly moist until germination.

Division is generally the quickest and most reliable method of producing new plants.

Cultural use:
The specific name inermis means “unarmed” or “without spines”, referring to the almost spineless seed heads that distinguish this species from other bidibids.

Its lack of troublesome hooked burrs has made it one of the most widely grown ornamental species of Acaena in New Zealand gardens.

Garden value:
Blue Mountain Bidibid is one of the best native groundcovers for pathways, courtyards and family gardens where ordinary bidibids may become a nuisance. Its attractive blue-grey foliage, seasonal purple tones and soft, nearly spineless seed heads provide year-round interest without the inconvenience of clinging burrs.

It is particularly valuable for alpine gardens, dry landscapes, gravel plantings and low-maintenance native gardens where a hardy, colourful groundcover is required.