Paleo-phyllotaxis: Fucales, bryophytes, lycophytes and monilophytes

Fibonacci spiral arrangements have evolved independently in brown algae, bryophytes, in lycophytes and euphyllophytes. “Non-Fibonacci spirals” have been described in Asteroxylon mackiei from the Rhynie chert and on the rhyzomes of lycopsid fossils (stigmaria) as well as several groups of living lycophytes and euphyllophytes. The occurrence of the same phyllotaxis patterns in phylogenetically distant groups and the rare spiral arrangements in early leafy plants are intriguing phenomena. We applied an inhibition model to brown algae and early diverging plants. We show that the same general physico-chemical processes that determine the position of primordia on meristems underlie spiral and whorled phyllotaxis in different lineages from brown algae to angiosperms. If Fibonacci spirals optimize light capture, “non-Fibonacci spirals” are in fact asymmetric whorls. The scales on the rhyzomes of lycopsids, which did not need to optimize their root-like appendage for photosynthesis, have this type of asymmetric whorled arrangement.