Development of the Lignotuber and Plant Form in Lehmannianae

Abstract

In lignotuberous species of the Lehmannianae, lignotuber formation is preceded by the appearance of a crescent-shaped array of accessory buds, adaxial to the axillary bud. Lignotubers may be formed at successive nodes but those with only one upper accessory bud (which may be present even in non- lignotuberous species) do not form lignotubers. The subsequent development of the lignotuber is described, as is the development of the seedling. Seedling shoot growth is characterized by indeterminate growth and, like that of the adult shoots, is sympodial. In well protected sites lignotuberous species may develop into small, single-stemmed trees but in harsher habitats death of the seedling shoot and its replacement from lignotuber buds result in enlargement of the lignotuber and enhance the tendency to adopt a mallee (many-stemmed) form.

Non-lignotuberous and lignotuberous species of the Lehmannianae occur side-by-side in habitats that are prone to fire. Lignotuberous species survive shoot-destructive vicissitudes, such as fire, by replacement from the lignotuber. Whereas flowering and fruiting of seedlings of lignotuberous species may be postponed for many years, seed production is precocious in the non-lignotuberous species of the series. This is regarded as an alternative adaptation to fire, which is one of the major factors of the habitats of the Lehmannianae. Even-aged pole stands of the non-lignotuberous species result from regeneration from seed, after fire. Following the production of gaps in the canopy and the thinning out of the stand, pole-stage trees assume their mature form by outgrowth of epicormic shoots, including some placed near the base of the trunk.