  Recent observations of coherence in photosynthetic complexes have led to the
question of whether quantum effects can occur in vivo, not under femtosecond
laser pulses but in incoherent sunlight and at steady state, and, if so,
whether the coherence explains the high exciton transfer efficiency. We
distinguish several types of coherence and show that although some
photosynthetic pathways are partially coherent processes, photosynthesis in
nature proceeds through stationary states. This distinction allows us to rule
out several mechanisms of transport enhancement in sunlight. In particular,
although they are crucial for understanding exciton transport, neither wavelike
motion nor microscopic coherence, on their own, enhance the efficiency. By
contrast, two partially coherent mechanisms---ENAQT and supertransfer---can
enhance transport even in sunlight and thus constitute motifs for the
optimisation of artificial sunlight harvesting. Finally, we clarify the
importance of ultrafast spectroscopy in understanding incoherent processes.
