The Mint Bush Family - Background

Introduction

The mint bush family, known as the Lamiaceae (formerly the Labiateae) is widespread throughout the world and contains a number of well-known, commercially cultivated plants which are used in cooking and for perfumes. These include:

  • Basil (Ocimum basilicum)
  • Culinary mints (Mentha species)
  • Lavender (Lavendula angustifolia)
  • Majoram and Oregano (Origanum species)
  • Rosemary (Rosmarinus officinalis)
  • Sage (Salvia officinalis)
  • Thyme (Thymus species)

Worldwide, the family compries over 200 genera and over 3000 species. There are about 20 Australian genera in the Lamiaceae, the best known of which are:

   3-lobed lower lip of the Lamiaceae
   The 2-lobed upper lip and the 3-lobed lower lip of the Lamiaceae is shown here in Hemiandra pungens.
 
   2-lipped calyx of Prostanthera
   The 2-lipped calyx (the green structure at the base of the flower) of Prostanthera is seen here in P.aspalathoides. Photos: Brian Walters
  • Ajuga; about 45 species worldwide, two native to Australia
  • Faradaya; about 18 species worldwide, one native to Australia
  • Hemiandra; about 7 species, all confined to Australia
  • Hemigenia; about 40 species, all confined to Australia
  • Mentha; about 20 species worldwide, about 6 native to Australia
  • Plectanthus; occurs in Africa, Asia and 15 species in Australia
  • Prostanthera; about 60-70 species, all confined to Australia
  • Scutellaria; about 300 species worldwide, 2 native to Australia
  • Westringia; about 23 species, all confined to Australia

The most commonly cultivated Australian members of the family are Prostanthera (known as "mint bushes"), Westringia and (occasionally) Hemiandra.

Characteristics

A characteristic of members of the Lamiaceae is a "two-lipped corolla" - in which the five petals are united into two upper lobes and three lower lobes giving the appearance of two lips. Although not a unique characteristic (eg. Eremophila in the Scrophulariaceae also have two lips), it is one of the easiest features to help the average person in identification. The two-lipped feature gave rise to the previous name for the family, the Labiateae (from Latin, labellum, a lip).

The two most popular genera in cultivation, Prostanthera and Westringia can be distinguished by the shape of the calyx at the base of the flower. In Prostanthera, the calyx is two-lipped while in Westringia the calyx is divided into 5 segments.

Members of the Lamiaceae are generally herbs and small to medium shrubs. In Australia, the only species which reaches small tree proportions is the Victorian Christmas tree (Prostanthera lasianthos) which can attain 8-9 metres in Gippsland forests.

Many members of the family have aromatic foliage due to the presence of volatile oils and it is these oils which give exotic members of the family their characteristic taste and aroma which is so valuable in cooking. In Australia, the genus with the most prounced aromatic foliage is Prostanthera (although not all species are aromatic). The foliage of many prostantheras emits a pleasant aroma when crushed or brushed against. In the Australian bush the aroma of mint bushes can be very pronounced following rain.

Despite the relatively high oil content of the foliage of many Australian members of the family, little use has been made of either the leaves or the oil. Some species are used by bush foods enthusiasts as flavourings in cooking in the same way as their exotic counterparts (eg. Mentha australis, Prostanthera rotundifolia).

In nature, members of the family can be found in a wide range of habitats..... coastal cliffs (Westringia fruticosa), semi alpine areas (Prostanthera monticola), semi arid areas (Hemiandra gardneri), rainforests (Prostanthera lasianthos). Some, like the Austral bugle (Ajuga australis), span a range of habitats over a wide area. Most species, however, are found as part of the understorey in open forests and woodlands.


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