Leptospermum 'Horizontalis'

(cultivar)

Family: Myrtaceae

 

A small spreading-sprawling shrub to about 1 metre tall by 2 to 3 metres wide.

It is reportedly a form of L. continentale, collected in heathland from Portland, Victoria in 1967. It was registered under this name in 1985.

There has been some confusion as to the heritage of this cultivar with early marketing labelled as Leptospermum juniperinum ‘Horizontalis’. It also has a history of being confused with L. scoparium. It has also been marketed as L. ‘Portlandii’

Plants can be dense, with dark green leaves, to 15 mm long and to 4 mm wide, slightly prickly.

Leptospermum typically produce solitary flowers, or in small groups of 2s and 3s or more, within the leaf axils. Flowers have 5 petals and sepals and have a symmetrical rotate shape.  Stamens are produced in groups of 5 which surround 1 carpel (female part). The prominent feature in Leptospermum is the hypanthium, a cup or vase-shaped receptacle that supports the flower.

In this cultivar, flowers are usually borne singularly on new growth, to 12 mm in diameter, with white or occasionally pink-flushed petals, occurring from Spring to Summer.

The fruit is a capsule to 8 mm wide with 5 valves and remaining on the plant when mature.

In the garden

This cultivar has been popular over the last few decades due to its ability to form a tall dense groundcover. It is hardy and tolerates a wide range of environments although may not thrive in tropical areas. It is suited to subtropical, temperate and cool climate gardens. 

It grows readily in a sandy to heavier, free-draining soil, and will benefit from some enrichment, in full sun to part shade. It may not thrive in boggy soils.

Can be pruned to create a dense plant, several metres across. Place in an area where it is free to spread out and be admired and where it has room to expand its ground-covering form.

It is recommended for rockeries and sloping beds. Can withstand dry periods.  

Leptospermum are generally susceptible to the webbing caterpillar. Usually, the most effective control method for this pest is removing infestations by hand or, if necessary, you can systematically spray with a suitable pesticide. They are also prone to scale insects which is best treated by spraying white oil solution.

Propagation

Must be propagated from cuttings to maintain form and characteristics.

Other information

Most Leptospermum species are endemic to Australia where most are found in southern areas of the country and many make desirable garden plants. Current estimates recognize about ninety species of Leptospermum along with many cultivars now existing.

The nectar from the flowers of one species (L. scoparium) is harvested by bees, yielding honey, which is marketed as Manuka honey.

Many Leptospermum species have an ability to regenerate vegetatively after fire with suckering basal growth and branch-shoots. They will also regenerate by seed.

The general common name, Teatree, derives from the practice of early Australian settlers who soaked the leaves of several species in boiling water to make a herbal tea.

Leptospermumderived from the Greek words leptos meaning “fine” or “slender” and sperma which means “seed” referring to the thin brown seeds of the genus.

‘Horizontalis’named for its sprawling and ground-covering habit.

Additional note: this style of naming for a cultivar, i.e. named in the form of a species epithet, is no longer permitted under the International Code of Botanical Nomenclature, due to its potential to cause much confusion.

Australian National Botanic Gardens – Leptospermum profile page https://www.anbg.gov.au/leptospermum/

Australian National Botanic Gardens – Leptospermum ‘Horizontalis’ profile page https://www.anbg.gov.au/acra/descriptions/acc372.html    

Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.

By Dan Clarke