Leptospermum scoparium J.R.Forst. & G.Forst. – horticultural cultivars

kahikātoa, mānuka, tea tree

Indigenous to New Zealand. In the current sense this species is also shared with Australia, particularly Tasmania. However, there is genetic evidence that mānuka in the strict sense is endemic to New Zealand. Further study is needed.

There is a long history of selections found from natural populations in New Zealand, and breeding programmes in New Zealand, Australia, California and Great Britain, to extend the range of form and flower colour. Recent work in New Zealand and Australia has successfully crossed different species. Popular in cultivation throughout New Zealand, especially cultivars with pink, red or double flowers. Some selections are being commercially developed for growing in plantations for claimed superior qualities in essential oil or honey production.

Leptospermum cultivars are cultivated in gardens throughout New Zealand.

• Leaf tips usually prickly and with rough margins.
• Flowers appearing solitary, greenish-white to pink-white, pink or red, single or double petalled.
• Sepals deciduous.
• Stamens shorter than petals.
• Fruit woody, persistent.
• Fruit valves forming a raised dome before opening.

Erect, dwarf or prostrate shrubs or small trees to about 5 m tall. High variation in form and flower characteristics of L. scoparium from New Zealand (rather than Australia) provided a wide range of parent traits to incorporate in crosses from which to select cultivars.

Bark grey, peeling in papery flakes. Young branchlets and stems hairy, becoming hairless with age.

Adult leaves alternate, narrowly elliptic or lanceolate to oblanceolate or obovate, variable in size, from less than 3 mm long in dwarf cultivars to ± 25 mm long in other cultivars, and less than 1 mm wide in dwarf cultivars to ± 10 mm wide in other cultivars; mostly prickly and sometimes soft to grasp, pale to dark green, leaf blade flat, leaf surfaces not puckered, some cultivars silky hairy, others hairy at first, becoming hairless, margins entire or finely scalloped, tips acute, leaf stalks very short (sometimes appearing absent).

Flowers solitary, axillary, usually 12–20 mm in diam. but up to 30 mm diam. in the tetraploid cultivar L. scoparium ‘Keatleyi’, petals 5 in single flowers, or more if double, some with frilly edges, greenish-white to white to pale or bright pink or red, single or double; sepals 5, stamens numerous, white to pink to red, shorter than the petals.

Fruit dry, persistent, woody, 5-locular, ± 5–7(–13) mm wide, valves domed, becoming very woody with age.

Mānuka (L. scoparium) and its hybrids are often confused with kānuka (Kunzea spp.), from which they can be easily distinguished by the hard, persistent, nut-like fruits, with non-persistent sepals, and flowers which appear to be solitary.

In garden situations, plants with bright-coloured or frilled petals or double flowers are almost certainly horticultural cultivars. Typical, naturally-occurring L. scoparium has simple 5-petalled white or pale pinkish flowers with a red centre. Leptospermum scoparium var. incanum is confined to the northern parts of the North Island and characterised by young branches, juvenile leaves and flower buds clad in long silky, grey hairs as well as mostly pink flowers.

Flower variants from New Zealand wild populations of typically white-flowered L. scoparium have provided genes for cultivars with white, pink and red flowers that are single or double, and plant forms ranging from prostrate groundcovers to upright shrubs.

More than 150 cultivars of L. scoparium have been named; some of the best include ‘Blossom’ (coral-pink double flowers), ‘Burgundy Queen’ (red double flowers, reddish foliage), ‘Crimson Glory’ (dark red double flowers, compact semi-dwarf, reddish foliage), ‘Keatleyi’ (large pink single flowers, large leaves), ‘Kiwi’ (red single flowers, dwarf growth form), ‘Martinii’ (pink single flowers darkening with age), ‘Red Damask’ (red double flowers, reddish foliage), and ‘Red Falls’ (red single flowers, prostrate growth form).

Australian species involved in crosses include showy-flowered species such as L. spectabile, L. rotundifolium, and L. macrocarpum.

In New Zealand L. scoparium is subject to attack by scale insects that secrete honeydew on which grows a sooty mould that eventually debilitates the plant. Because of this, attempts have been made to cross the showy New Zealand cultivars with scale insect resistant Australian Leptospermum species. Double-flowered, single-flowered, dwarf and pendulous plants have been selected; resistance to mānuka blight and improved vase life for the cut flower industry were also objectives.

Leptospermum is a genus of about 87 species, mostly Australian, but extending to Malesia and New Zealand.

• CitSciHub (species profile)
• CitSciHub (prostrate cultivar)
• CitSciHub (L. scoparium ‘Blossom’)
• Flora of New Zealand Online (L. scoparium var. incanum)
• Flora of New Zealand Online (L. scoparium var. scoparium)
• GBIF
• iNaturalist NZ (L. scoparium var. incanum)
• iNaturalist NZ (L. scoparium var. scoparium)
• NZPCN (L. scoparium var. incanum)
• NZPCN (L. scoparium var. scoparium)