Laboratory of Molecular Systematics & Evolutionary Genetics
Ancient seeds spill secrets about the evolution of flowering plants.
by Matthew Gitzendanner
Figure 1 | Seed evolution. Shi et al.1 present fossil evidence that sheds light on a long-standing mystery about the origin of the protective layer, termed the outer integument (or second integument), that surrounds the seeds of flowering plants (angiosperms). It is thought that flowering plants arose from now-extinct plants belonging to a group called the gymnosperms (living members of which include conifers). a, Gymnosperms have one integument that surrounds the embryo of a seed. A structure called the cupule, which might have provided protection or aided seed dispersal, formed the outer layer of ancient gymnosperm seeds. b, Flowering plants have inner and outer integuments. Shi and colleagues find that the cupule probably evolved to form the outer integument of flowering plants. Angiosperm seeds are connected to the carpel structure that surrounds them through a stalk called the funiculus. Shi and colleagues suggest that the funiculus evolved from the stalk of the gymnosperm cupule.
The origin and rapid diversification of flowering plants is a long-standing “abominable mystery”, as Charles Darwin put it. Part of the puzzle – the origin of the protective covering of flowering-plant seeds – is nearing resolution.
