Nectaries in ferns: their taxonomic distribution, structure, function, and sugar composition.

Area of Science:

• Plant Biology
• Evolutionary Biology
• Ecology

Background:

• Extrafloral nectaries (EFNs) are primarily studied in flowering plants (angiosperms).
• Previous research identified EFNs in 39 fern species, suggesting a broader occurrence.
• Ferns represent an ancient lineage, making their EFNs of significant evolutionary interest.

Purpose of the Study:

• To conduct a global review of nectaries in ferns.
• To investigate the structure, function, and nectar composition of EFNs in two fern genera.
• To understand the evolutionary origins and ecological roles of fern EFNs.

Main Methods:

• Literature review and examination of living plant collections to identify fern nectaries.
• Morphoanatomical studies of nectaries in the genera Aglaomorpha and Campyloneurum.
• Analysis of nectar sugar concentration and composition in 16 fern species.
• Time-lapse photography to observe diurnal nectar release patterns.

Main Results:

• Evidence for EFNs was found in 101 fern species across 11 genera and 6 families.
• Tree ferns (Cyatheaceae) and epiphytic ferns (Polypodiaceae) were most frequently nectary-bearing.
• Nectaries featured parenchyma cells and an epidermis, releasing nectar primarily at night on expanding leaves; nectar sugar varied (3.8-15.3% total sugars).

Conclusions:

• The widespread distribution and varied characteristics of fern nectaries suggest multiple independent evolutionary origins.
• Nectar production on young leaves may attract protective mutualists, such as ants, during vulnerable growth stages.
• Fern nectar serves as a valuable food resource for various opportunistic animal species, even in ex-situ collections.