Re: Why would a plant have two different kinds of fruit?

Sorry for the delay, but I had never seen this plant and it took me a long 
time to get the information. I found 3 interesting references for this 
plant in the scientific literature.
The interesting thing is that there are 3 different fruits in this plant. 
One of them is buried, and the other two are aerial (exposed to the air) 
and these are the ones you see. The fruits you see have a very important 
difference: the higher one is pollinated with pollen from other individual, 
while the other is self-pollinated. This means that the one close to the 
ground bears less genetic variation, and the other carries genes (genetic 
material) from two different individuals. The one buried is also 
self-pollinated.
There are also differences in seed size, speed of maturation of the fruits, 
and so forth..
All these strategies are used for one obvious objective: to leave in the 
world as many "sons" as possible. This incredible variations is a guaranty 
that at least one of these strategies will be adequate for the survival of 
the next generation.
It is very common inplants to spread its strategies over a wide range of 
possibilities instead of concentrating in an specific "approach". If the 
enviroment changes and this "approach" becomes inadequate, the hole species 
may extinguish. This heappens all the time. That is why dinossaurs are 
dead.
Mail me if you need more explanations or take a look in the references 
below:
TRAPP EJ, HENDRIX SD
     CONSEQUENCES OF A MIXED REPRODUCTIVE-SYSTEM IN THE HOG PEANUT,
     AMPHICARPAEA-BRACTEATA, (FABACEAE)
     OECOLOGIA 75: (2) 285-290 1988 

and
TRAPP EJ
     DISPERSAL OF HETEROMORPHIC SEEDS IN AMPHICARPAEA-BRACTEATA (FABACEAE)
     AM J BOT 75: (10) 1535-1539 OCT 1988 
and
SCHNEE BK, WALLER DM
     REPRODUCTIVE-BEHAVIOR OF AMPHICARPAEA-BRACTEATA (LEGUMINOSAE), AN 
AMPHICARPIC ANNUAL
     AM J BOT 73: (3) 376-386 MAR 1986