Ecology of the early angiosperms

A re-appraisal of the ecology of the early angiosperms has yielded surprising results. T. S. Feild and colleagues took the latest cladistic analysis of early angiosperms, and grew their closest living relatives in experimental gardens. It turned out that almost all these living plants grew best in environments that were shady, not sunny, and in disturbed rather than stable soils. This result was so surprising that no-one had ever suggested it before, and it demands that we re-think the conditions in which the early angiosperms evolved.

The only important plants in the study that do not have this habitat preference are water-lilies, which of course are aquatic (and it is also important that Archaefructus, the earliest angiosperm, happens to look aquatic too). However, water-lilies look as if they evolved in shady habitats, and their aquatic habitat may be a secondary evolutionary step. Overall, "dark and disturbed" seems to define the habitat of early angiosperms: banks of forest streams, shady places along river banks, and so on.

Living "basal" angiosperms have relatively small seeds (that can fall into cracks in disturbed ground), and are more than normally capable of spreading by creeping shoots and roots. They live in comparatively damp environments and have cell shapes in their leaves that scatter low light efficiently into the leaf structure rather than passing it through. As far as one can tell, the fossil evidence from early Cretaceous angiosperms is compatible with the dark disturbed hypothesis, but we are talking about microhabitats and the geological evidence does not allow a precise test of the idea (yet).

If the hypothesis is true, it could explain how angiosperms found a way to flourish in a pre-existing Mesozoic flora: they occupied a habitat in which there was not much competition. It fits with the idea that angiosperms were comparatively rapid reproducers, quickly able to colonize disturbed patches of forest floor. It explains why early angiosperms have been difficult to study: they were small and ephemeral, ecological "weeds". Only later, as angiosperms adjusted to more stable, sunny environments, did they become larger, more easily fossilizable, and more prominent in paleobotanical collections.

Feild, T. S., et al. 2004. Dark and disturbed: a new image of early angiosperm ecology. Paleobiology 30: 82-107.

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Drafted by RC October 5, 2004.