Protasparagus densiflorus: an environmental weed of coastal vegetation reserves

Abstract

Protasparagus densiflorus, a native of southern Africa, has become established in Australian coastal vegetation from Noosa Heads to Batehaven, a range of at least 1 200 km of the coast of eastern Australia. Plants fruit prolifically, the seeds have no endogenous dormancy, and are viable while the fruit is still immature. Germination is retarded in the light when compared with that in the dark, but temperature fluctuations appear not to influence germination rates. When exposed to a 9°C day-night temperature variation germination was successful in the range of minimum temperatures from 9° to 26°C, with an apparent optimum at 23°C. Temperatures suited to germination are therefore available to the species in every month of the year in a coastal subtropical climate. Tubers formed on the roots of seedlings 9?14 days after germination. Tubers increased the probability of plants surviving air-dry for six days on plants which were 16 days old. Detailed studies in two small coastal conservation reserves in southeastern Queensland showed different distribution patterns. Dispersal of the species appears to be anthropogenic, by birds and perhaps by lizards. Protasparagus densiflorus is a threat to the conservation value of coastal vegetation in some of the most densely populated regions of eastern Australia.