Sundew

Botanical name: Drosera arcturi
Synonyms: Drosera polyneura, Drosera ruahinensis, Drosera ligulata, Drosera atra
Common name(s): Sundew, Alpine Sundew

About:
Drosera arcturi is a small perennial carnivorous herb of cool montane, subalpine and alpine wetlands. It forms compact rosettes of narrow leaves covered with glistening, sticky glands that trap small insects. The plant supplements the limited nutrients available in acidic bog soils by digesting captured prey. During winter it retreats into a tightly folded dormant bud, or hibernaculum, which may remain beneath moss, shallow water or snow until spring.

Natural habitat:
Occurs in montane to alpine bogs, peatlands, seepages and wet herbfields. It frequently grows around the margins of tarns, shallow pools, burn pools and slow-flowing streams draining bogs.

In the southern part of its range it may descend to sea level, particularly in cold, wet districts. Plants often grow among sphagnum moss or in permanently saturated peat and may form scattered colonies in shallow water.

Growing environment:
Requires cool conditions, very high moisture and acidic, nutrient-poor soil. It grows in full sun or bright open conditions where its foliage may develop deep red or maroon colouring.

The root zone must remain constantly wet with clean, low-mineral water. It is intolerant of fertiliser, lime, alkaline soil, ordinary potting mix and mineral-rich tap water.

Endemic distribution:
Indigenous but not endemic to New Zealand. Found in the North, South and Stewart Island/Rakiura from the central North Island axial ranges and volcanic plateau southwards. It also occurs in south-eastern Australia and Tasmania.

Height:
Leaves generally 1–7 cm tall; flowering stems may reach approximately 5–25 cm

Width:
Approximately 2–10 cm per rosette, with colonies sometimes spreading more widely

Flowering:
November–April

Fruiting:
November–April, most commonly from summer into early autumn

Uses:
• Specialist carnivorous plant collections
• Alpine and wetland botanical displays
• Educational planting
• Conservation and wetland restoration
• Study of carnivorous plant ecology

Appearance:
Growth habit:
A small, clump-forming perennial herb arising from a short stock surrounded by the remains of old leaf bases. Plants often grow as individual rosettes or in loose colonies among moss and wet peat.

Leaves:
Leaves are upright to spreading, narrow and strap-like, generally 1–7 cm long. The lower portion is smooth and somewhat sheathing, while the upper surface is covered with stalked glandular hairs.

Leaf colour varies from pale green and olive-brown to reddish-brown or deep maroon. Plants exposed to strong sunlight usually develop the deepest colouring.

Young leaves emerge tightly folded along the centre. As they mature, they open outward in a manner resembling a book.

Carnivorous glands:
The leaf surface bears numerous reddish glandular hairs tipped with sticky mucilage. Small insects become trapped when they contact the droplets. Nearby glands and portions of the leaf may slowly move toward the prey, after which digestive enzymes release nutrients that are absorbed through the leaf surface.

Flowers:
Flowers are usually solitary, although one to three may occasionally be produced on an upright, leafless stem. The flowers are white, approximately 10–16 mm across, with broad ovate to obovate petals.

In high-altitude plants, the flowering stem is commonly short and positions the flower near or just above the leaves. Larger lowland forms may produce several flowers on stems reaching approximately 25 cm.

Fruit:
The fruit is an elongated dry capsule, commonly around 1 cm long. It splits when mature to release numerous minute seeds.

Seeds:
Seeds are extremely small and are dispersed primarily by wind, with water movement also likely assisting local dispersal through wetland habitats.

Ecology:
Sundew is adapted to strongly acidic wetlands where nitrogen and other nutrients are scarce. Its carnivorous leaves allow it to obtain additional nutrients from small flies, midges and other invertebrates.

The plant contributes to the specialised flora of alpine bogs, tarn margins and sphagnum wetlands. It may grow alongside bladderworts and other small wetland herbs occupying similarly nutrient-poor conditions.

Growth is strongly seasonal. New upright leaves emerge in spring, followed by flowering during summer. As temperatures fall, the leaves become progressively shorter and fold together to form an elongated, horn-like hibernaculum. This dormant structure protects the growing point through freezing temperatures, snow cover and prolonged winter saturation.

Associated habitats:
Sphagnum bogs, alpine tarn margins, peatlands, seepages, burn pools, wet herbfields, boggy stream margins and shallow alpine pools. Associated species may include sphagnum mosses, sedges, rushes, cushion plants, alpine herbs and native bladderworts such as Utricularia dichotoma.

How to grow:
Grow in a cool, sunny position using an acidic, nutrient-poor medium such as unmilled sphagnum moss or a carefully prepared mixture of peat and washed silica sand.

Keep the container permanently moist by standing it in a shallow tray of rainwater, distilled water or reverse-osmosis water during active growth. Never use fertiliser, compost, lime or ordinary garden soil.

Plants require a cool winter dormancy. During this period the foliage may disappear almost completely as the plant contracts into its hibernaculum. The growing medium should remain moist but not stagnant.

This species is difficult to cultivate in warm climates and generally performs best where summers are mild and winters are cold.

Propagation:
Propagation is primarily from fresh seed. Sow onto the surface of wet sphagnum or an acidic peat-and-sand medium without covering deeply, as light assists germination.

Seed may benefit from a prolonged period of cold, moist stratification that mimics natural winter conditions. Germination can be slow and irregular, and seedlings require consistently cool, humid conditions.

Established clumps may sometimes produce additional growing points that can be separated, but disturbance should be kept to a minimum. Wild plants must never be removed.

Cultural use:
No specific traditional Māori uses are widely documented for this species. Its unusual insect-trapping leaves make it an important educational example of adaptation to nutrient-poor wetland environments.

The name Drosera is derived from a Greek word meaning “dewy”, referring to the sparkling mucilage droplets on the leaves. The specific name arcturi refers to Mount Arthur in Tasmania, the type locality from which the species was first described.

Garden value:
A fascinating specialist plant for cool-climate carnivorous collections, alpine houses and carefully managed bog gardens. Its glistening red glands, seasonal colour changes and delicate white flowers provide considerable interest despite its very small size.

Because it requires cold winters, permanently clean water and nutrient-poor acidic conditions, it is best suited to experienced growers and specialised conservation collections.