Lamiaceae

(Labiatae)

Common names : mint or sage family

Image of Mentha longifolia Photo: G Nichols
Mentha longifolia © G Nichols

Intro sentence
The Lamiaceae family is characterized by square stems, aromatic leaves (gland-dotted) and zygomorphic (irregular) flowers with the corolla usually 2-lipped. It is a cosmopolitan family with many well-known members of horticultural and economic importance such as Mentha longifolia.

Description
The species of Lamiaceae are mainly herbs or shrubs of various sizes, rarely trees. Life cycles of the herbaceous members may be annular or perennial. The stems are usually square, especially when young, erect or procumbent (lying on the ground). The leaves are opposite or whorled, decussate (in opposite pairs, with each pair at right angles to the one above and below it), and gland-dotted. The leaves are often strongly aromatic due to ethereal oils located in the glandular hairs. The leaf blades are simple, rarely pinnately lobed (Teucrium) or digitately compound (Cedronella, Vitex), with entire or toothed margins. The flowers are arranged in compact axillary cymes (verticillasters), e.g. in the white Leonotis, or are sometimes single in the axils of the leaves. Sometimes the inflorescences are congested as in Pycnostachys. The calyces are usually persistent with 5 teeth or lobes. Zygomorphic (irregular) flowers are very characteristic of the family. However, actinomorphic (regular), 4-or 5-lobed flowers occur in some genera. The corolla is tubular and typically 2-lipped (bilabiate) with a 2-lobed upper lip and a 3-lobed lower lip, variously coloured and often hairy. The flowers are bisexual, rarely unisexual. The stamens are usually 4 (2 long and 2 short ones), arising at the corolla mouth or in the tube and characteristically exserted from the corolla tube (Hemizygia). Sometimes the filaments are connate (cannot be separated). A superior ovary seated on an entire or lobed disc is characteristic with the style gynobasic (arising from the base of the pistil) or terminal.

Image of White Leonotis

White Leonotis

Image of Pycnostachys

Pycnostachys

Image of Hemizygia Photo: G Nichols
Hemizygia © G Nichols

The fruits are composed of 4, or by abortion fewer, dry, 1-seeded nutlets, or may be a drupe with 1-4 pyrenes, subtended by or enclosed within a persistent calyx. The outer surface of the nutlets may be smooth or rugose (wrinkled). Occasionally the nutlets are winged (Tinnea).

Distribution
Worldwide the Lamiaceae, a member of the seed-forming, dicotyledonous plants, comprises over 240 genera and 6 500 species, following the family circumscription of Cantino et al. (1992). The main centre of diversity is the Mediterranean region to central Asia. Members are found in tropical and temperate regions. About 60 genera with ± 980 species occur in the Sub-Saharan African region (Klopper et al. 2006). In South Africa, there are ± 255 species in 35 genera. The species occur predominantly in the summer rainfall areas, but are also found in the winter rainfall areas. The habitats vary to a great extent. The species inhabit not only dry, often rocky, woodland or grassland, but also occur along forest margins and in fynbos.

Conservation status
Many species of Lamiaceae are currently not threatened. However, habitats in which they occur are threatened by human impact and thus may change their status in future. Many species are endemic to a restricted area, and are regarded as rare because of their narrow distribution but are not considered as threatened at this stage, for example, Syncolostemon macranthus, known from the Natal Drakensberg between Cathedral Peak and Van Reenen's Pass and just extending into the eastern Free State.

Derivation of name and historical aspects
The family was established by De Jussieu in 1789 as the Order Labiatae. The name Labiatae alludes to the flowers typically having petals fused into an upper and lower lip, the flower thus having an open mouth! Although Labiatae is an acceptable, alternate name, botanists more often use Lamiaceae after the genus Lamium. The family is divided into several subfamilies and tribes of which subfamily Nepetoideae has the most genera. The Lamiaceae is closely related to the family Verbenaceae. Several recent, phylogenetic studies have shown that some genera classified in Verbenaceae belong, however, in Lamiaceae, for example, Vitex and Clerodendrum. Salvia is the largest genus of the family, representing ± a 1 000 species, differing remarkably in their morphology.

Image of Salvia
Salvia

Ecology
Members are strongly adapted for bird pollination. They are important for providing nectar and pollen to support bee colonies.

Economic and cultural value
Lamiaceae is characterized by aromatic plants which have been widely used since ancient times. The family is known for culinary herbs such as basil, mint, oregano, rosemary, sage and thyme. Members are a source of essential oils for the flavouring and perfume industry, for example, the widely cultivated lavender, Lavandula. The Zulu tribe of South Africa calls Leonotis leonurus, utschwalabenyoni, meaning the beer of birds, referring to the copious nectar produced by the plant which is relished by sunbirds.

Image of Plectranthus
Plectranthus

Growing plants of the Lamiaceae family
Many species of the Lamiaceae are attractive to grow in the garden, for example, the genus Plectranthus. Leonotis leonurus is grown as an ornamental in various parts of the world. Plants are easily propagated from stem cuttings. Ocimum, an important economic and medicinal herb, requires warmth for growth and should be protected from frost. Visit the search page to search for several other members of the Lamiaceae already written about on this site, for example, Plectranthus, Ballota and Salvia.

References and further reading
  • Cantino, P.D., Harley, R.M. & Wagstaff, S.J. 1992. Genera of Lamiaceae: status and classification. In R.M. Harley & T. Reynolds, Advances in Labiate Science : 511-522. Royal Botanic Gardens, Kew.
  • Codd, L.E. 1985. Lamiaceae. In O.A. Leistner, Flora of southern Africa 28: 1-247. Botanical Research Institute, Pretoria.
  • Germishuizen, G., Meyer, N.L., Steenkamp, Y. & Keith, M. (eds). 2006. A checklist of South African plants. Southern African Botanical Diversity Network Report No. 41. SABONET, Pretoria.
  • Klopper, R.R., Chatelain, C., Bänninger, V., Habashi, C., Steyn, H.M., De Wet, B.C., Arnold, T.H., Gautier, L., Smith, G.F. & Spichiger, R. 2006. Checklist of the flowering plants of Sub-Saharan Africa. An index of accepted names and synonyms. Southern African Botanical Diversity Network Report No. 42. SABONET, Pretoria.
  • Van Jaarsvled, E.J.& Edwards, T.J. 1997. Notes of Plectranthus (Lamiaceae) from southern Africa. Bothalia 27(1):1-6
  • Van Wyk, B-E. 2005. Food plants of the world: identification, culinary uses and nutritional value. Briza Publications, Pretoria.

 

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