ECOLOGY OF ASCLEPIAD LIANES 
97 
Fig. 5. Seeds and young seedlings of Marsdenia australis (A-D) and Rhyncharrhena linearis (E-G). A, E, dry 
seeds with comas. B, seed with radicle 2 days after sowing. C, F, seedlings 7 days after sowing showing root hairs. 
D, G, seedlings 12 days after sowing. Scale bars = 3 mm. 
secondary roots (Fig. 6A) when the shoots are 
440 mm tall. 
On exceeding about 150 mm in height, the 
stem is unable to support the weight of the ex¬ 
panding leaves and bows over to become nearly 
horizontal; lateral shoots then develop from 
lower nodes. At this stage, the distal part of 
shoots can begin to revolve dextrorsely and to 
twine around any support encountered. Without 
support, the stem may bow almost to the ground 
and twine up about itself. 
Rhyncharrhena seeds are rugulose, dull 
brown, flattened and elliptical to oblong. Germi¬ 
nation and young seedling morphology are as for 
Marsdenia except for longer, denser root hairs 
and narrow-elliptical cotyledons (Fig. 5). No 
problem with persistent testas was found. 
At 18 weeks, a root system lacking tubers is 
present (Fig. 6B); stem growth is similar to Mars- 
denia. There is no obvious ontogenetic change in 
leaf shape in either species. 
Adult morphology 
Shoots. Both species have opposite leaves lighter 
green and with denser stomata on the abaxial 
than on the adaxial surface. The stomata are 
modified rubiaceous type (Metcalfe & Chalk 
1957). 
Stem diameter was typically 5-7 mm and up 
to 10 mm in Marsdenia , but only 3 to 5 mm in 
Rhyncharrhena. When no support is found by 
circumnutating stems of either species, the 
stems can twine around themselves. In Mars¬ 
denia this can result in tightly plaited ropes up to 
6 m long (Fig. 7); similar stems occur in the as- 
clepiad Araujia sericofera (Menninger 1970). 
Like most Australian asclepiads, Marsdenia 
and Rhyncharrhena are apical stem twiners, a 
type of behaviour said to be seldom effective in 
climbing trees of over 100 mm diameter at 
breast height (Hegarty & Clifford 1984). In this 
study, we found them twining up a range of 
