106 
KATHY M. NICHOLS, J. H. BROWNE AND R. F. PARSONS 
It is much more common for flowers of both 
species to wither and fall than to produce fruit; 
this can happen to Rhyncharrhena when Mars¬ 
denia is still flowering and fruiting at the same 
site. Although Rhyncharrhena flowered a num¬ 
ber of times from 1981 to 1990, only five fruits 
(containing a total of 177 seeds) could be found, 
one in 1982 and four in 1989-90. Other than 
this, the only Rhyncharrhena fruiting records we 
know of are: (a) June 1950, after exceptional 
February-March rainfall of 177 mm (E. Ram¬ 
say, unpublished manuscript); and (b) March 
1976, after exceptional October-December 
rainfall of 225 mm (our data). Finding as many 
as four fruits in 1989-90 was not due to heavy 
rain but because we started to examine re¬ 
peatedly 48 adult plants; (a) and (b) above may 
indicate that appreciable levels of fruiting only 
follow exceptional rains. 
Marsdenia fruiting is more common; for 
example 18 fruits could be found in 1984 and in 
1990 38 adult plants under observation pro¬ 
duced 15 fruits. 
Number of seeds per fruit ranged from 37 to 
213 for Marsdenia and 18 to 78 for Rhynchar¬ 
rhena. Individual Marsdenia flowers remain 
open for seven to ten days and those of 
Rhyncharrhena for two to three days. This com¬ 
pares with five to six days for Asclepias meadii 
(Betz 1989), seven to eight days for A. tuberosa 
(Wyatt 1981) and 10-15 days for Fischeria fun- 
ebris (Skutch 1988). 
General phenology, 1989-1990. Following rain 
falls of 125 mm from 14 March to 7 April 1989, 
Rhyncharrhena , but not Marsdenia , flowered in 
mid-April. Virtually all these flowers were shed 
in late April without setting fruit. 
No further flowering of either species oc¬ 
curred until above-average rain of 54 mm from 6 
November to 2 December. By 14 December, 
shoot growth and flowering occurred profusely 
in all full-grown Marsdenia plants but not in any 
Rhyncharrhena plants. 
In this area, 10 mm is the minimum rainfall 
that most farmers regard as being significant for 
plant growth in summer. There were no falls this 
large between 3 December 1989 and 21 April 
1990. On 2 January 1990, with temperature 
maxima about 40°C, all Rhyncharrhena plants 
were either wilted or had started losing leaves. 
This was not true of Marsdenia except for some 
wilted sucker shoots. However, on 3 January 
1990 temperatures reached 47°C, the hottest for 
50 years; nearly all Marsdenia wilted and shed 
their flowers except for those at site 3. The plants 
at site 3 shed most of their flowers a few days 
later. By 11 January, most Marsdenia shoots had 
recovered without damage. Between then and 25 
January new shoot growth was noted iotMars- 
denia but not for Rhyncharrhena which showed 
further leaf loss and stem death and did not re¬ 
cover until April. 
It was possible to obtain a few mature fruits 
of both species in January 1990; those of 
Rhyncharrhena probably arose from the April 
1989 flowering while the origin of the Marsdenia 
fruits is unknown. 
Detailed studies. At site 1, small flower buds 
were present on some plants of both species, 
especially Rhyncharrhena , before watering 
started. A second crop of Rhyncharrhena buds 
was present on 15 May following substantial 
rains. Despite these buds, throughout the work 
only a single plant of either species was seen with 
open flowers, a Rhyncharrhena in early March, 
and no fruit was set. Plants of both species, both 
watered and unwatered, showed some increase 
in shoot length and leaf number from February 
to September. This was most marked during 
April and May. The overall increases in mean 
shoot length to 4 August 1990 were: Rhynchar¬ 
rhena (watered) 473 mm, Rhyncharrhena 
(unwatered) 133 mm, Marsdenia (watered) 197 
mm and Marsdenia (unwatered) 229 mm. Al¬ 
though there was no statistically significant ef¬ 
fect of watering, more data may have confirmed 
that Rhyncharrhena responds more strongly to 
watering than Marsdenia. 
Events at the other sites from February' to Sep¬ 
tember 1990 were generally similar to those 
at site 1.. The very few Rhyncharrhena that 
flowered included two plants at site 2 on 22 
March, possibly in response to the artificial 
watering. The only Marsdenia to flower were 
three plants at site 5 on 6 March following 17 
mm of rain. Despite the widespread Marsdenia 
flowering of December 1989, only at site 3 did 
fruit set occur, with a total of 10 fruits. A fruit cut 
open in June contained only immature seeds, 
while seeds from one cut open in August gave 
100% germination. The remaining fruits finally 
opened naturally in mid-November 1990. This 
period of 11 months from flowering to seed re¬ 
lease compares with tw r o to four months from 
flowering to fruiting for Sarcostemma esculen- 
tum and Gymnema geminatum (Forster 1989) 
and about 3.5 months from pollination until 
fruits are ripe in Asclepias meadii (Betz 1989). 
