Metrosideros diffusa (G.Forst.) Sm.

rātā, white climbing rātā, white rātā

New Zealand endemic.

Not widely grown in cultivation but may be occasionally available from specialist native plant nurseries. There is one accepted cultivar, the variegated-leaved Metrosideros diffusa ‘Crystal Showers’.

Coastal to montane throughout the North and South Islands of New Zealand.

• Climber.
• Leaves ranked on either side of stem and lie in one plane.
• Juvenile leaves upper surface hairless to sparsely hairy.
• Adult leaves <25 mm long.
• Midvein and lateral veins raised.
• Flowers axillary along the branches and not terminal.
• Flowers white or occasionally pink.
• Calyx tube narrower than fruit (± 1 mm wide).

Slender vines up to ± 6 m when supported, often forming a tangled bushy shrub up to 1 m tall on the forest floor (especially in riparian forest).

Bark rusty red-brown to grey, separating into thick, squarish flakes. Branchlets round to indistinctly 4-angled, with short brown hairs, often branching dichotomously.

Leaves opposite, ranked on either side of stem and lie in one plane, oblong to ovate-lanceolate to ovate-oblong, 15–25 mm long, 7–12 mm wide upper surface bright to dark glossy green, paler below, leaf surface flat, not puckered, upper and lower surfaces hairless, oil glands visible on both surfaces, but more so below; margins entire and slightly recurved, lightly hairy; tips rounded or pointed; leaf stalks absent or very short, hairy.

Flower clusters borne laterally along the branches on the previous season’s woody stem, never from the new shoot, not terminally; cluster-branchlets often 3-flowered, or flowers solitary on cluster axis. Flowers ± 10 mm in diam., flower stalks ± 3–4 mm long, petals 5, white sometimes flushed pink; sepals 5, tips free, persistent, with scattered hairs, margins more conspicuously hairy; stamens mostly white, sometimes flushed pink, filaments 7–9 mm long. Main flowering period: late spring to summer.

Fruit dry, rounded, ± 3–4 mm wide, capsule dome occurring below the persistent calyx tube, calyx tube narrower than fruit (± 1 mm wide), capsule splits along sides to release seeds.

Sterile material similar to M. colensoi, but M. diffusa differs in that leaves are at right-angles to the branch, juvenile leaves are similar in colour to adult leaves, young upper leaf surfaces are hairless to very sparsely hairy, and the midveins and lateral veins are prominently raised. In M. colensoi, the young growth is pale yellow-green, the leaves are held an acute angle to the branch, the juvenile leaves are hairy on the upper surface and the midvein and lateral veins are not prominently raised. Flower clusters in M. diffusa occur laterally along branches, whereas they occur terminally in M. colensoi.

Foliage of the exotic, opposite-leaved garden plants Lonicera nitida (hedge honeysuckle) and Buxus sempervirens (box) is also very similar. Both are commonly used as hedge plants throughout New Zealand, and have naturalised in a few places where they sometimes grow with M. diffusa. Lonicera nitida has young branchlets purple, thickly covered in fine hairs plus a few bristly hairs, cream fragrant flowers usually in pairs in leaf axils, and fruit a translucent purple berry. Buxus sempervirens has leaves not usually lying in one plane, and tiny, pale yellow flowers crowded into tight clusters in the leaf axils. These are followed by a rounded berry-like capsule 6–10 mm long with three horn-like projections.

Metrosideros diffusa was given a conservation status of Threatened – Nationally Vulnerable in 2018. It is now known that M. diffusa is susceptible to myrtle rust (caused by Austropuccinia psidii) and in some places (Bay of Plenty, Waikato, Taranaki) this vine is now in decline.

Metrosideros is a genus of more than 50 species of trees, shrubs and vines, mostly found in the Pacific region. New Zealand is well represented by having 12 endemic species.

• Flora of New Zealand Online
• GBIF
• iNaturalist NZ
• NZPCN