Aston's Willowherb (Epilobium astonii) hero image

Aston's Willowherb

Epilobium astonii

At Risk - Naturally Uncommon

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Aston's willowherb (Epilobium astonii) is a heavily branched, bushy willowherb that forms compact clumps up to about 30 cm tall and wide, with the whole plant covered in sticky glandular hairs. Its nodding flowers are white, flushing pink after pollination, and appear from December to February. It is endemic to the North Island's main axial ranges, from the Raukumara Range south to the northern Ruahine Range, growing on greywacke cliffs, gorge walls and exposed ridge-top boulders at 760 to 1370 m. It is ranked At Risk - Naturally Uncommon because of its narrow range, though it is common where it occurs. Explore more native flowering plants in our native plant guide.

Aston's Willowherb (Epilobium astonii) in its natural habitat
Image credit: Aston's Willowherb (Epilobium astonii) - photo by Wikipedia contributors, via Wikipedia

Plant Description

Epilobium astonii is an erect, heavily branched perennial herb forming compact bushes up to about 300 mm tall and 300 mm across. The whole plant is hairy, with a mixture of erect plain and glandular hairs, and the stems are glandular-hairy all over. The leaves are opposite or nearly so (alternate in the flowering part), dull green, narrowly obovate with a pointed tip, 13 to 33 mm long and 7 to 15 mm wide, with finely toothed margins bearing 8 to 24 small teeth and three lateral veins on each side. The leaf stalks are 2 to 6 mm long with fine wings.

The flowers and flowering shoots nod. Petals are white, flushing pink after pollination, 7.3 to 13 mm long, with sepals 5 to 6.5 mm long. Flowering is from December to February and fruiting from January to April, when the long capsules split to release seeds carrying tufts of silky hairs.

Its closest relative is Epilobium pubens, from which it was originally described as a variety. E. pubens is slender and scarcely branched with much smaller sepals (2.5 to 2.8 mm) and petals (3.5 to 7 mm), and it is widespread rather than confined to high greywacke rock.

Quick Facts

Epilobium astonii quick facts
Scientific Name Epilobium astonii
Height 0.09-0.3 m
Spread Up to 0.3 m
Water Needs Low; quite drought tolerant
Light Full sun
Frost Tolerance High; subalpine to alpine
Salt Tolerance No information available
Growth Rate Moderate
Lifespan Perennial

Climate Best Suited to

Suits cool, montane to subalpine climates with good air movement. It dislikes high humidity, so it is poorly suited to warm, muggy lowland gardens.

Regional Suitability

City suitability for Epilobium astonii
City Climate Suitability
Auckland Low
Wellington Medium
Christchurch Medium
Dunedin Medium

Plant Habitat

Aston's willowherb is endemic to the main axial ranges of the North Island, from the high points of the Raukumara Range south to the northern Ruahine Range. Recorded sites include Mount Hikurangi and Mount Honokawa in the Raukumara Range, the Kaimanawa Mountains and the Mangaohane Stream area of the Ruahine Range.

It is a subalpine to alpine plant of 760 to 1370 m, growing on greywacke and also limestone, typically on cliff faces, canyon and gorge walls and exposed boulders on ridgelines, where it forms colonies very locally.

Growing Requirements

Soil Requirements

In the wild it roots into crevices and thin soil on greywacke and limestone rock faces.

  • Very free-draining, gritty soil
  • Rock crevices and stony ground
  • Low to moderate fertility

Light Requirements

It grows on exposed cliffs and ridges and does best in full sun.

  • Full sun
  • Open, airy position

Water Requirements

NZPCN notes that it is quite drought tolerant, reflecting its rock-face habitat where water drains away quickly.

  • Water sparingly once established
  • Avoid wet, poorly drained soil
  • Keep foliage dry in humid weather

Planting and Establishing

Plant Aston's willowherb in a rock garden, crevice bed, scree or pot with very free-draining, gritty mix in full sun. A spot with good airflow is important because it dislikes high humidity.

Raised beds and troughs work well in wetter districts, and a stone-chip mulch keeps the base of the plant dry.

Ecological Role

On cliffs and gorge walls, Aston's willowherb is part of a specialised rock-face flora where few competitors can establish. Its plumed seeds are suited to wind dispersal, allowing it to reach new ledges and crevices.

The insects that pollinate its nodding white flowers are not recorded in the sources consulted.

Uses & Significance

Garden Uses

NZPCN describes it as easily grown, making it one of the more garden-worthy rare willowherbs.

  • Rock and crevice gardens
  • Alpine troughs and pots
  • Collections of rare North Island endemics

Ecological Value

It is a narrow-range endemic of the North Island axial ranges and part of the distinctive cliff flora of the Raukumara, Kaimanawa and Ruahine Ranges.

  • Endemic to a small part of the North Island
  • Colonises cliff faces and gorge walls
  • Cultivated plants provide a backup to wild populations

Landscaping Uses

Use Aston's willowherb as a small, rounded accent plant among rocks, where its dull green, sticky foliage and nodding white to pink flowers stand out against grey stone.

It pairs well with other small alpine natives in troughs and scree beds that share its need for sharp drainage and sun.

Seasonal Care Calendar

Spring

New growth develops on the compact bushy clumps.

  • Trim away any dead stems
  • Top-dress with grit

Summer

Flowering runs from December to February, with nodding white flowers that turn pink after pollination.

  • Water only in prolonged drought
  • Ensure good airflow in humid weather

Autumn

Capsules ripen from January to April and release plumed seed.

  • Collect seed as capsules split
  • Sow fresh

Winter

Plants tolerate cold and frost on their mountain cliffs.

  • Keep potted plants out of persistent wet
  • No feeding needed

When to Prune and How Much

Little pruning is required. Cut back spent flowering stems after seed has been shed to keep the clump compact.

Remove any dead or rotting shoots from the base, especially after wet, humid spells.

How to Grow Aston's Willowherb

NZPCN notes that Aston's willowherb is easily grown in a pot or rock garden in full sun, that it dislikes high humidity and that it is quite drought tolerant, but it does not describe a specific propagation method. Seed is the natural starting point, since plants flower from December to February and ripen capsules from January to April, and willowherb seed usually germinates readily when fresh. Cuttings of non-flowering shoots are also worth trying, as with other bushy willowherbs. Because this is a narrow-range endemic ranked At Risk, use seed or cuttings from cultivated plants rather than collecting on its cliffs, which are in any case difficult and dangerous to reach. Grow young plants in a gritty, very free-draining mix with plenty of light and air movement to avoid rot and mildew.

From Seed

Collect capsules from cultivated plants as they start to split in late summer or autumn.

  1. Gather capsules as they begin to split
  2. Sow seed fresh on the surface of a gritty seed mix
  3. Lightly press in and keep just moist
  4. Place in bright light with good ventilation
  5. Pot seedlings individually into gritty mix once they have a few leaf pairs

From Cuttings

Short non-flowering shoots can be rooted in spring or early summer.

  1. Take 3 to 5 cm cuttings of non-flowering shoots
  2. Remove the lower leaves
  3. Insert into a mix of pumice and fine bark
  4. Keep lightly moist and out of hot sun, without enclosing in a humid case
  5. Pot on once roots have formed

Pests & Diseases

No specific pests are recorded for Aston's willowherb. In cultivation the main problems are rot and mildew in humid or poorly drained conditions.

In the wild its cliff habitat protects it from most browsing, and no specific threats are documented in the sources consulted beyond its naturally narrow range.

Cultural Significance

No traditional Māori name or use is recorded for Epilobium astonii in the sources consulted.

It was first described by H.H. Allan in 1961 as a variety of Epilobium pubens and was raised to a separate species by Peter Raven and Tamra Engelhorn in 1971. The species name honours a collector named Aston; the sources consulted do not give further details.

Bonus Tip

If your plant becomes leggy or rots in a humid summer, grow it in a clay pot of pure grit and pumice placed where breezes blow through, and water from below. This mimics the dry, airy cliff faces where it grows naturally.

Plant Conservation

Epilobium astonii is ranked At Risk - Naturally Uncommon (2023) because of its narrow range and limited geographic extent, although NZPCN regards it as common where it occurs.

Much of its habitat lies in conservation land in the Raukumara, Kaimanawa and Ruahine Ranges. Keeping weeds and browsing animals in check in these ranges, and maintaining plants in cultivation, help secure it.

Frequently Asked Questions

Where does Aston's willowherb grow?

It is endemic to the North Island's main ranges, recorded from Mount Hikurangi and Mount Honokawa in the Raukumara Range, the Kaimanawa Mountains and the Mangaohane Stream area of the Ruahine Range, at 760 to 1370 m.

How is Epilobium astonii different from Epilobium pubens?

Aston's willowherb is a much larger, compact, bushy plant, whereas E. pubens is slender and scarcely branched. It also has longer sepals (5 to 6.5 mm) and petals (7.3 to 13 mm), and is restricted to subalpine greywacke rock habitats.

Can you grow Aston's willowherb in a garden?

Yes. NZPCN says it is easily grown in a pot or rock garden in full sun, is quite drought tolerant and dislikes high humidity.

Sources and Further Reading

The botanical, growing, and conservation details for Aston's Willowherb (Epilobium astonii) on this page draw on the New Zealand plant references below. Consult them for full technical records and the latest distribution data.