Comparison of a common, rare and declining plant species in the Asteraceae: possible causes of rarity

Abstract

Three forbs of contrasting abundance were compared with the aim of identifying ecological traits that may be associated with differences in abundance in Australia. Hypochoeris radicata (an extremely common, exotic species), Cymbonotus lawsonianus (rare in some regions, moderately common in others) and Microseris lanceolata (once widespread but which has dramatically declined) are all species of grasslands and grassy woodlands. Habitat details and phenological observations are reported from the New England Tablelands, New South Wales where the three species co-occur. This information is synthesized with that available in the literature. Part of the success of H. radicata relates to its broad environmental tolerance. Although C. lawsonianus and M. lanceolata are both widely distributed in Australia, the range of habitats in which they occur is more limited. The depletion of M. lanceolata populations is largely attributed to a vulnerability to domestic grazing animals that may be linked to its palatability and architecture. The more common C. lawsonianus and H. radicata appear more tolerant of grazing and mowing and may be advantaged by their ability to form flat rosettes. Despite its occurrence at sites with soil disturbance, C. lawsonianus is still rare in comparison with H. radicata. It may be restricted by a lack of phenotypic plasticity that prevents plants adopting an erect leaf position under more competitive situations. A number of rare native herbs appear to be disturbance-dependent, and it is suggested that C. lawsonianus may share with them highly specific ecological requirements that make both undisturbed and human-disturbed sites sub-optimal for their persistence.