ECOLOGY OF ASCLEPIAD LIANES 
107 
The period from pollination to seed release for 
three species of Asclepias ranges from about 2 to 
4.5 months (Kephart 1987). 
With increasing temperatures in September, 
most mature Marsdenia and Rhyncharrhena 
plants produced new crops of flower buds. The 
driest spring on record ensued (15 mm of rain at 
Mildura) and December was also very dry 
(4 mm). All Rhyncharrhena flower buds were 
lost but Marsdenia showed widespread flower¬ 
ing by mid-November. With very high January 
rainfall (87 mm), some flowers produced a crop 
( of fruits 5 mm in diameter by 12 January and 
these became virtually full-sized by 2 February. 
A total of 49 full-sized fruits were counted at 
sites 1 and 3 on 13 February' 1991. 
By contrast, it was only after the 29 mm of 
rainfall on 5 January that Rhyncharrhena 
flowered (Fig. 16). It is assumed that this flower¬ 
ing produced the 20 well-developed fruits found 
at site 1 on 11 February'. In central Australia, for 
both species, “significant fruiting only occurs 
after exceptional seasons or after fire” (P. K. 
Latz, personal communication). 
The timing of events in Marsdenia is consist¬ 
ent over large areas; around Lindsay Point, 115 
km to the west-north-west, Marsdenia also shed 
its seeds and flowered in November 1990 (R. 
Stoeckel, personal communication). 
A major difference between Marsdenia and 
Rhyncharrhena is that in hot, dry periods during 
summer and autumn 1990 virtually all 
Rhyncharrhena plants lost at least some of their 
leaves, while no Marsdenia plants did. This was 
even more noticeable in the very dry late spring 
of 1990 when the few remaining Rhyncharrhena 
leaves were yellow and wilted while all Mars¬ 
denia leaves were still present and in good 
condition. The partial deciduousness of Rhyn¬ 
charrhena may aid survival during drought 
(Russell-Smith & Dunlop 1987). While Marsde¬ 
nia is regarded by Pate & Dixon (1982) as semi- 
deciduous if drought-stressed, we have never 
seen leaf loss at any time. Perhaps leaf loss oc¬ 
curs only in the most extreme conditions, poss¬ 
ibly as a prelude to stem death (P. K. Latz, 
personal communication). 
Although it is said that Rhyncharrhena can be 
- 4 ^- 
l.R.1. 
% 16. Monthly rainfall (Red Cliffs), monthly means for daily maximum temperatures (Mildura), flowering 
imesfor Marsdenia australis and Rhyncharrhena linearis , and growth rate (shoot elongation) for unwatered R. 
lineans shoots at site 1 from February to September 1990. 
