Diurnal Lhc gene expression is present in many but not all species of the plant kingdom.

The diurnal and circadian expression of light-harvesting genes (Lhc) is well documented for many plant species of the 'Angiospermae' division. Here we present the diurnal mRNA levels of species of the Gymnospermae, Pteridophyta, Bryophyta and Phycophyta divisions. Except for four Coniferophytina species, diurnal Lhc mRNA accumulation is detected in fern, moss and algae, supporting the idea that the concept of 'ciracadian clock'-controlled gene expression is an ancient process. Possible reasons why plants need the 'circadian clock' control mechanism are discussed.