MORGAN, DAVID R.1* and KENNETH R. ROBERTSON2. 1Department of Biology, Western Washington University, Bellingham, WA 98225; 2Illinois Natural History Survey, Champaign, IL 61820. - Fruit evolution in Rosaceae.
The traditional view of fruit evolution in Rosaceae hypothesized that
follicles were the ancestral fruit type and that pomes, drupes, and
achenes were derived from follicles, each type originating once.
Recent phylogenetic evidence suggests relationships that do not
support this traditional view of fruit evolution. According to recent
evidence, species that have many carpels per flower and that have
one-seeded indehiscent fruits ("achenes") cluster at the
base of Rosaceae, suggesting that the fruits of the ancestors of
Rosaceae had these characteristics. This evidence also suggests that
some types of fruits may have originated multiple times as similar
modifications to the ancestral fruit type occurred in separate
lineages. One major lineage supported by recent evidence is Rosoideae
s.s., in which the one-seeded indehiscent fruit type was retained but
in which several receptacular modifications appeared. In the remainder
of Rosaceae, evolution of fruits appears to have been more complex.
Modifications that resulted in dehiscent fruits having two or more
seeds ("follicles") may have occurred more than once. Other
modifications to the ancestral type resulted in fruits that were still
one-seeded and indehiscent but that had thick pericarps with hard
endocarps and fleshy or fibrous mesocarps ("drupes"). These
kinds of modifications may also have arisen multiple times. The pome
fruits characteristic of subfamily Maloideae appear to have arisen as
a result of two independent events. The first was the development of
an expanded hypanthium that enclosed the carpels at maturity, and the
second was the development of fleshiness in the expanded hypanthium.
Key words: fruit evolution, Rosaceae phylogeny, Rosaceae