INTRODUCTION - Tropical Fruits - page 5

increased the ei ciency of angiosperm seed dispersal. Climate change,
radiation of birds and animals, and changes in plant community habitats are
all potential evolutionary forces that led to the appearance of a range of fruit
types. The fl eshy fruits, with their mutually benefi cial interaction of providing
nutrition to animals and improving seed dispersal, have arisen independently
in dif erent families, have disappeared and reappeared, are not evolutionarily
conserved, and show no clear association with phylogeny. The fossil and
morphological evidence indicates that multiple fruit types have evolved
directly from a dry follicle-bearing ancestor (Fig. 1.1).
The follicle is seen as the archetypical progenitor fruit, with a single
fused carpel that splits along a single seam (dehiscent zone). The fused carpel
appeared about 97 million years ago (Mya), in the middle Cretaceous. The
abscission (separation) zones are found much earlier in the fossil record
(400 Mya) in early vascular plants. In fruit, the biochemical processes in the
dehiscence zones and during ripening are thought to have co-opted systems
that evolved for the abscission of sporangia, leaves, petals and stamens. The
fruits that are consumed have soft and juicy arils (rambutan, litchi, longan),
pedicel (cashew), fl oral and accessory tissue (pineapple, annonas), mesocarp
Fig. 1.1. Types and structures of tropical fruits and their evolutionary development
from dehiscent and non-dehiscent dry fruits (redrawn from fi gures in Nakasone and
Paull, 1998).