94 
KATHY M. NICHOLS, J. H. BROWNE AND R. F. PARSONS 
Fig. I. Fruiting Marsdenia australis growing on Do- 
donaea viscosa at site 3 in March 1991. 
two species of Marsdenia and one of Tylophora 
in the rainforests and adjacent tall open-forests 
of East Gippsland 600 km to the south-east. 
The aim of this paper is to provide an intro¬ 
duction to the ecology of two asclepiads of arid 
and semi-arid areas, Marsdenia australis (Fig. 1) 
and Rhyncharrhena linearis (Fig. 2), at the tem¬ 
perate, southern limit of their range in Australia. 
Rhyncharrhena is one of only four asclepiad 
genera endemic to Australia, while Marsdenia is 
one of the most widespread genera, extending 
through parts of Asia, Africa and America. It is 
assumed that both M. australis and R. linearis 
were derived from northern Australian rain¬ 
forest taxa in response to increasing aridity 
(Beadle 1981). 
The work, nearly all in Victoria, is based on 
sporadic field observations from 1981 to 1989 
and intensive work from January to December 
1990. For brevity, the species will be referred to 
simply by their generic names. Two reasons for 
the project are (1) that both species have a con- 
Fig. 2. Fruiting Rhyncharrhena linearis growing on 
Dodonaea viscosa at site 1 in March 1991. 
servation status rated as vulnerable Victoria¬ 
wide (Gullan, Cheal & Walsh 1990) so that data 
are needed as a basis for their management, and 
(2) that both were important aboriginal foods 
(Latz 1982) and Marsdenia in particular may be 
worth cultivating for its palatable fruits and its 
use as an indoor plant (Cherikoff & Isaacs no 
date, V. Cherikoff personal communication). 
DISTRIBUTION AND HABITAT 
Both species occur in inland parts of all main¬ 
land states of Australia including Queensland 
(Cunningham et al. 1981, Queensland Herbar¬ 
ium unpublished). There are records of both 
from at least as far north as 20°S, about the lati¬ 
tude of Tennant Creek (P. Latz personal com¬ 
munication) to as far south as 35 C S near 
Walpeup in northwestern Victoria (this study). 
Mean annual rainfall for both species can 
range from below 150 mm in the Great Victoria 
Desert (Greenslade, Joseph & Barley 1986) to 
above 400 mm in central New South Wales 
(Wilson 1980, Royal Botanic Gardens Sydney 
1989). Seasonal rainfall distribution shows a 
slight May to October peak in Victoria (Badawy 
1982) but changes to a summer maximum which 
becomes progressively more marked north¬ 
wards (Slatyer 1962). 
The whole area experiences hot summers and 
mild winters; mean temperatures increase 
steadily northwards. While frosts are very rare to 
absent north of 21°30', mean annual frost 
frequency ranges from 7 to 32 in the area from 
Alice Springs to northwestern Victoria without 
correlating closely with latitude (Slatyer 1962, 
Australian Bureau of Meteorology unpublished 
data). Mean length of frost season is more 
