With fronds like these… foliar dimorphism and reproduction in ferns

Far from being a simple process, reproduction can be a complex and costly venture. Obtaining the proper balance between reproduction, growth, and maintenance can lead to compromises in form and function. In the case of flowering plants, sexual reproduction is largely constrained to highly specialized flowers and fruits, focusing reproductive efforts in one organ.

Movement of 13C-labelled gas throughout Osmundastrum cinnamomeum and Osmunda regalis across the growing season. — Movement of ¹³C-labelled gas throughout *Osmundastrum cinnamomeum* and *Osmunda regalis* across the growing season. Plants were labelled with ¹³C-labelled CO₂ gas three times during the growing season (May, June and August), and collected at the end of the growing seasons before senescence. Whole plants were collected and divided into constituent parts: sterile fronds, fertile fronds, rhizomes and roots . In *O. cinnamomeum*, there is no evidence of translocation of labelled carbon from the labelled sterile frond to any part of the plant in May. Plants that were labelled in June show a large translocation of carbon to the rhizome. Plants labelled in August maintain very little of the fixed labelled carbon in the labelled frond, with most of the signal being found translocated to the rhizome. There was no evidence of translocation of fixed carbon to the fertile fronds or the roots. In *O. regalis* there is no evidence of translocation of labelled carbon from the labelled sterile fronds to any other part of the plant in both May and June. In August, there is evidence of translocation from the sterile frond to the rhizome, but no evidence of translocation to the fertile fronds or the roots.

Ferns pose a unique set of challenges as they use the leaf as the site of both reproduction and carbon fixation. Britton and Watkins examine two cases of extreme foliar dimorphism in ferns and find that fertile-sterile dimorphy comes at considerable carbon costs to ferns likely influencing species ecology. A potential benefit of such costs is increased spore dispersal distance and more fine-tuned control over frond phenology.