ECOLOGY OF TWO ASCLEPIAD LIANES IN SEMI-ARID VICTORIA 
Kathy M. Nichols 1 , J. H. Browne 2 and R. F. Parsons 1 
'Botany Department, La Trobe University. Bundoora, Victoria 3083 
2 52A Fitzroy Avenue, Red Cliffs. Victoria 3496 
Nichols, K. M„ Browne, J. H. & Parsons, R. F., 1991:12:31. Ecology of two asclepiad 
lianes in Victoria. Proceedings of the Royal Society of Victoria 103 (2): 93-112. ISSN 
0035-9211. 
Marsdenia australis and Rhyncharrhena linearis (Asclepiadaceae) are lianes of the “thin 
wiry” type. In Victoria they are found in semi-arid woodlands, secondary' shrublands and 
mallee communities. Both can sucker profusely from the roots to form large clones but only 
Marsdenia has tuberous roots. Both species have a pair of foliar glands per leaf adaxially at 
the leaf base. 
Fresh seed of both species has high germinability and most germinated in a few days, 
especially at 25°C. Germinability of Marsdenia seed declines with time and is zero at 14 yr. 
At 18 weeks old, Marsdenia seedlings have higher dry weights than those of Rhyncharrhena 
due to their well-developed tuberous root systems. 
Although both species flower annually, there is regular Novembcr-Dccember Mars¬ 
denia flowering, even in very dry conditions, whereas only a few' Rhyncharrhena flowered 
after heavy rain within the January-April period during our study. Fruit set was low for both 
species, especially Rhyncharrhena. Both species showed some increase in shoot length from 
February to September; this is most rapid when rain falls during w r arm w-eather. During 
drought, Rhyncharrhena plants rapidly lost leaves while Marsdenia plants did not. Tuberous 
roots may allow Marsdenia to flower, fruit and retain leaves in conditions too dry for such 
behaviour in Rhyncharrhena. Both species are now vulnerable in Victoria. It is thought that 
the main threat is grazing by stock and rabbits. Fruiting has only been seen in plants which 
are climbing above 0.5 m in shrubs or trees; deliberate introduction of long-lived woody 
plants is needed to ensure seed production of Marsdenia and Rhyncharrhena in some grazing 
exclosures. 
THE ASCLEPIADACEAE is a predominantly 
pan-tropical family of about 2000 species, 
mostly of woody climbers, perennial herbs and 
shrubs. The 60-odd Australian species occur 
mainly in the east and north, especially in rain¬ 
forest, but a few species are widespread in semi- 
arid to arid areas and reach temperate latitudes 
(Williams 1984). Of the 12 or so important dico¬ 
tyledonous liane families, Asclepiadaceae and 
Convolvulaceae (see below) are two which es¬ 
pecially spread beyond rainforests into season¬ 
ally dry' areas, both in Australia and elsewhere 
(Forster 1988, Hegarty 1989, Vahrmeijer 1981). 
Lianes show decreasing robustness with de¬ 
creasing annual rainfall; those dealt with here 
belong to the most slender of Webb’s (1978) 
liane categories, being normally present as the 
thin wiry'” type (stem diameters less than 10 
mm). In semi-arid north-western Victoria, there 
are seven native species which could be con¬ 
sidered under this heading: Marsdenia australis 
and Rhyncharrhena linearis (Asclepiadaceae), 
Jasminum didymum ssp. lineare (Oleaceae), 
Cematis microphylla (Ranunculaceae) and 
Convolvulus crispifolius, C. erubescens and C. 
remotus (Convolvulaceae). Species nomen¬ 
clature follows Ross (1990) except that the name 
Marsdenia australis (R. Br.) Druce has been pre¬ 
ferred to Leichardtia australis R. Br. following 
recent revisionary studies suggesting that 
Leichardtia is a synonym of Marsdenia (P. I. 
Forster personal communication). Inclusion of 
the Convolvulus spp. on the above list may be 
contentious as similar Convolvulus species are 
treated by some authors as herbaceous, not 
woodv, climbers (Pate & Dixon 1982, Keeley & 
Keeley 1988). 
Of Australian asclepiads, only a small number 
of species from Cynanchum , Marsdenia, 
Rhyncharrhena and Sarcostemma occur in semi- 
arid to arid regions. They show various features 
thought to be xeromorphic, like leaflessness and 
succulence {Sarcostemma) or reduced leaves 
(e.g. Rhyncharrhena) (Lapinpuro 1976). The 
only such species occurring in Victoria, to be 
dealt with in detail below, are Marsdenia aus¬ 
tralis and Rhyncharrhena linearis. Other than 
these, the only native asclepiads in Victoria are 
93 
